485BPOS

As filed with the Securities and Exchange Commission on May 21, 2015

Securities Act Registration No. 2-34223

Investment Company Act File No. 811-1829

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Post-Effective Amendment No. 102

and

REGISTRATION STATEMENT

UNDER

THE INVESTMENT COMPANY ACT OF 1940

Amendment No. 77

COLUMBIA ACORN TRUST

227 West Monroe Street, Suite 3000

Chicago, Illinois 60606

Telephone number: 312.634.9200

Scott R. Plummer c/o Columbia Management Investment Advisers, LLC 225 Franklin Street Boston, MA 02110	P. Zachary Egan Columbia Acorn Trust 227 West Monroe Street, Suite 3000 Chicago, Illinois 60606	Mary C. Moynihan Perkins Coie LLP 700 13th Street, N.W., Suite 600 Washington, D.C. 20005
(Agents for service)

It is proposed that this filing will become effective:

x immediately upon filing pursuant to rule 485(b)

¨ on                     pursuant to rule 485(b)

¨ 60 days after filing pursuant to rule 485(a)(1)

¨ on                      pursuant to rule 485(a)(l)

¨ 75 days after filing pursuant to rule 485(a)(2)

¨ on                      pursuant to rule 485(a)(2).

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all the requirements for effectiveness of this post-effective amendment pursuant to Rule 485(b) under the Securities Act of 1933 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Chicago and State of Illinois on May 21, 2015.

COLUMBIA ACORN TRUST
By	/S/    P. ZACHARY EGAN
	P. Zachary Egan, President

Pursuant to the requirements of the Securities Act of 1933, this amendment to the registration statement has been signed below by the following persons in the capacities and on the dates indicated.

Name	Title		Date
/S/    LAURA M. BORN	Trustee and Chair	)
Laura M. Born		)
		)
/S/    MAUREEN M. CULHANE	Trustee	)
Maureen M. Culhane		)
		)
/S/    MARGARET M. EISEN	Trustee	)
Margaret M. Eisen		)
		)
/S/    THOMAS M. GOLDSTEIN	Trustee	)
Thomas M. Goldstein		)
		)
/S/    JOHN C. HEATON	Trustee	)
John C. Heaton		)
		)
/S/    STEVEN N. KAPLAN	Trustee	)
Steven N. Kaplan		)
		)
/S/    CHARLES R. PHILLIPS	Trustee	)
Charles R. Phillips		)
		)
/S/    DAVID J. RUDIS	Trustee	)	May 21, 2015
David J. Rudis		)
		)
/S/    P. ZACHARY EGAN	Trustee and President (principal executive	)
P. Zachary Egan	officer)	)
		)
/S/    JOHN M. KUNKA	Treasurer (principal financial and	)
John M. Kunka	accounting officer)	)

Index of Exhibits Filed with this Amendment

Exhibit No.	Description
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2015
Columbia Acorn International
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY OF THE FUND
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Columbia Acorn International® (the Fund) seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 21 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 28% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	28.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 21 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that: you invest $10,000 in the applicable class of Fund shares for the periods indicated, your investment has a 5% return each year, and the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal circumstances, the Fund invests at least 75% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil). Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $5 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $5 billion at the time of initial investment. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Investment Manager typically seeks companies with: A strong business franchise that offers growth potential. Products and services in which the company has a competitive advantage. A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company. The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down. Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives. Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies. Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility. Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar. Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers. Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking. Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations. Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations. Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Liquidity and Trading Volume Risk. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance. Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility. Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar. Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors.
Risk Lose Money [Text]	rr_RiskLoseMoney	There is no assurance that the Fund will achieve its investment objective and you may lose money.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with those of the Standard & Poor’s (S&P) Global Ex-U.S. Between $500 Million and $5 Billion® Index, the Fund’s primary benchmark, the S&P Global Ex-U.S. SmallCap® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap® Index is provided to show how the Fund’s performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund’s primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund’s performance compares to a widely recognized broad based index of foreign market performance. The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities. The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares. The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with those of the Standard & Poor’s (S&P) Global Ex-U.S. Between $500 Million and $5 Billion® Index, the Fund’s primary benchmark, the S&P Global Ex-U.S. SmallCap® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap® Index is provided to show how the Fund’s performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund’s primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund’s performance compares to a widely recognized broad based index of foreign market performance.
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	The table below the bar chart compares the Fund’s returns for the periods shown with those of the Standard & Poor’s (S&P) Global Ex-U.S. Between $500 Million and $5 Billion® Index, the Fund’s primary benchmark, the S&P Global Ex-U.S. SmallCap® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap® Index is provided to show how the Fund’s performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund’s primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund’s performance compares to a widely recognized broad based index of foreign market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800.345.6611
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	columbiathreadneedle.com/us
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Year by Year Total Return (%) as of December 31 Each Year
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best and Worst Quarterly Returns During the Period Shown in the Bar Chart Best                            2nd Quarter 2009                            33.30% Worst                         3rd Quarter 2008                            -23.68%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs).
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	The after-tax returns are shown only for Class Z shares and will vary for other share classes.
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.
Columbia Acorn International | Class A
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[1]
Management fees	rr_ManagementFeesOverAssets	0.75%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.26%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.26%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	696
3 years	rr_ExpenseExampleYear03	952
5 years	rr_ExpenseExampleYear05	1,227
10 years	rr_ExpenseExampleYear10	2,010
1 year	rr_ExpenseExampleNoRedemptionYear01	696
3 years	rr_ExpenseExampleNoRedemptionYear03	952
5 years	rr_ExpenseExampleNoRedemptionYear05	1,227
10 years	rr_ExpenseExampleNoRedemptionYear10	2,010
1 Year	rr_AverageAnnualReturnYear01	(10.05%)
5 Years	rr_AverageAnnualReturnYear05	6.84%
10 Years	rr_AverageAnnualReturnYear10	7.95%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn International | Class B
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	5.00%	[2]
Management fees	rr_ManagementFeesOverAssets	0.75%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.75%
Other expenses	rr_OtherExpensesOverAssets	0.50%
Total annual Fund operating expenses	rr_ExpensesOverAssets	2.00%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge decreases over time.
1 year	rr_ExpenseExampleYear01	703
3 years	rr_ExpenseExampleYear03	927
5 years	rr_ExpenseExampleYear05	1,278
10 years	rr_ExpenseExampleYear10	2,136
1 year	rr_ExpenseExampleNoRedemptionYear01	203
3 years	rr_ExpenseExampleNoRedemptionYear03	627
5 years	rr_ExpenseExampleNoRedemptionYear05	1,078
10 years	rr_ExpenseExampleNoRedemptionYear10	2,136
1 Year	rr_AverageAnnualReturnYear01	(9.75%)
5 Years	rr_AverageAnnualReturnYear05	7.06%
10 Years	rr_AverageAnnualReturnYear10	7.87%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn International | Class C
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[3]
Management fees	rr_ManagementFeesOverAssets	0.75%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.23%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.98%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge applies to redemptions within one year after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	301
3 years	rr_ExpenseExampleYear03	621
5 years	rr_ExpenseExampleYear05	1,068
10 years	rr_ExpenseExampleYear10	2,306
1 year	rr_ExpenseExampleNoRedemptionYear01	201
3 years	rr_ExpenseExampleNoRedemptionYear03	621
5 years	rr_ExpenseExampleNoRedemptionYear05	1,068
10 years	rr_ExpenseExampleNoRedemptionYear10	2,306
1 Year	rr_AverageAnnualReturnYear01	(6.16%)
5 Years	rr_AverageAnnualReturnYear05	7.31%
10 Years	rr_AverageAnnualReturnYear10	7.76%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn International | Class I
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.75%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.10%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.85%
1 year	rr_ExpenseExampleYear01	87
3 years	rr_ExpenseExampleYear03	271
5 years	rr_ExpenseExampleYear05	471
10 years	rr_ExpenseExampleYear10	1,049
1 year	rr_ExpenseExampleNoRedemptionYear01	87
3 years	rr_ExpenseExampleNoRedemptionYear03	271
5 years	rr_ExpenseExampleNoRedemptionYear05	471
10 years	rr_ExpenseExampleNoRedemptionYear10	1,049
1 Year	rr_AverageAnnualReturnYear01	(4.20%)
5 Years	rr_AverageAnnualReturnYear05	8.54%
10 Years	rr_AverageAnnualReturnYear10	8.99%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 27, 2010
Columbia Acorn International | Class R
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.75%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other expenses	rr_OtherExpensesOverAssets	0.37%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.62%
1 year	rr_ExpenseExampleYear01	165
3 years	rr_ExpenseExampleYear03	511
5 years	rr_ExpenseExampleYear05	881
10 years	rr_ExpenseExampleYear10	1,922
1 year	rr_ExpenseExampleNoRedemptionYear01	165
3 years	rr_ExpenseExampleNoRedemptionYear03	511
5 years	rr_ExpenseExampleNoRedemptionYear05	881
10 years	rr_ExpenseExampleNoRedemptionYear10	1,922
1 Year	rr_AverageAnnualReturnYear01	(4.95%)
5 Years	rr_AverageAnnualReturnYear05	7.76%
10 Years	rr_AverageAnnualReturnYear10	8.26%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 02, 2011
Columbia Acorn International | Class R4
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.75%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.28%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.03%
1 year	rr_ExpenseExampleYear01	105
3 years	rr_ExpenseExampleYear03	328
5 years	rr_ExpenseExampleYear05	569
10 years	rr_ExpenseExampleYear10	1,259
1 year	rr_ExpenseExampleNoRedemptionYear01	105
3 years	rr_ExpenseExampleNoRedemptionYear03	328
5 years	rr_ExpenseExampleNoRedemptionYear05	569
10 years	rr_ExpenseExampleNoRedemptionYear10	1,259
1 Year	rr_AverageAnnualReturnYear01	(4.39%)
5 Years	rr_AverageAnnualReturnYear05	8.43%
10 Years	rr_AverageAnnualReturnYear10	8.94%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn International | Class R5
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.75%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.15%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.90%
1 year	rr_ExpenseExampleYear01	92
3 years	rr_ExpenseExampleYear03	287
5 years	rr_ExpenseExampleYear05	498
10 years	rr_ExpenseExampleYear10	1,108
1 year	rr_ExpenseExampleNoRedemptionYear01	92
3 years	rr_ExpenseExampleNoRedemptionYear03	287
5 years	rr_ExpenseExampleNoRedemptionYear05	498
10 years	rr_ExpenseExampleNoRedemptionYear10	1,108
1 Year	rr_AverageAnnualReturnYear01	(4.25%)
5 Years	rr_AverageAnnualReturnYear05	8.48%
10 Years	rr_AverageAnnualReturnYear10	8.95%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 02, 2011
Columbia Acorn International | Class Y
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.75%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.10%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.85%
1 year	rr_ExpenseExampleYear01	87
3 years	rr_ExpenseExampleYear03	271
5 years	rr_ExpenseExampleYear05	471
10 years	rr_ExpenseExampleYear10	1,049
1 year	rr_ExpenseExampleNoRedemptionYear01	87
3 years	rr_ExpenseExampleNoRedemptionYear03	271
5 years	rr_ExpenseExampleNoRedemptionYear05	471
10 years	rr_ExpenseExampleNoRedemptionYear10	1,049
1 Year	rr_AverageAnnualReturnYear01	(4.21%)
5 Years	rr_AverageAnnualReturnYear05	8.50%
10 Years	rr_AverageAnnualReturnYear10	8.97%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn International | Class Z
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.75%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.18%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.93%
1 year	rr_ExpenseExampleYear01	95
3 years	rr_ExpenseExampleYear03	296
5 years	rr_ExpenseExampleYear05	515
10 years	rr_ExpenseExampleYear10	1,143
1 year	rr_ExpenseExampleNoRedemptionYear01	95
3 years	rr_ExpenseExampleNoRedemptionYear03	296
5 years	rr_ExpenseExampleNoRedemptionYear05	515
10 years	rr_ExpenseExampleNoRedemptionYear10	1,143
2005	rr_AnnualReturn2005	21.81%	[4]
2006	rr_AnnualReturn2006	34.53%	[4]
2007	rr_AnnualReturn2007	17.28%	[4]
2008	rr_AnnualReturn2008	(45.89%)	[4]
2009	rr_AnnualReturn2009	50.97%	[4]
2010	rr_AnnualReturn2010	22.70%	[4]
2011	rr_AnnualReturn2011	(14.06%)	[4]
2012	rr_AnnualReturn2012	21.60%	[4]
2013	rr_AnnualReturn2013	22.33%	[4]
2014	rr_AnnualReturn2014	(4.28%)	[4]
Year to Date Return, Label	rr_YearToDateReturnLabel	Year to Date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2015
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	4.34%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	33.30%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(23.68%)
1 Year	rr_AverageAnnualReturnYear01	(4.28%)
5 Years	rr_AverageAnnualReturnYear05	8.47%
10 Years	rr_AverageAnnualReturnYear10	8.95%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 23, 1992
Columbia Acorn International | returns after taxes on distributions | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(5.65%)
5 Years	rr_AverageAnnualReturnYear05	7.55%
10 Years	rr_AverageAnnualReturnYear10	8.06%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 23, 1992
Columbia Acorn International | returns after taxes on distributions and sale of Fund shares | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(0.99%)
5 Years	rr_AverageAnnualReturnYear05	6.76%
10 Years	rr_AverageAnnualReturnYear10	7.49%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 23, 1992
Columbia Acorn International | S&P Global ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(1.76%)
5 Years	rr_AverageAnnualReturnYear05	7.14%
10 Years	rr_AverageAnnualReturnYear10	7.65%
Columbia Acorn International | S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(3.11%)
5 Years	rr_AverageAnnualReturnYear05	7.41%
10 Years	rr_AverageAnnualReturnYear10	7.27%
Columbia Acorn International | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(4.90%)
5 Years	rr_AverageAnnualReturnYear05	5.33%
10 Years	rr_AverageAnnualReturnYear10	4.43%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge decreases over time.

[3] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[4] Year to Date return as of March 31, 2015: 4.34%

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2015
Columbia Acorn USA
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY OF THE FUND
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Columbia Acorn USA® (the Fund) seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 17 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 12% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	12.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 17 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that: you invest $10,000 in the applicable class of Fund shares for the periods indicated, your investment has a 5% return each year, and the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal circumstances, the Fund invests at least 80% of its net assets (including the amount any borrowings for investment purposes) in U.S. companies. Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $5 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $5 billion at the time of initial investment. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Investment Manager typically seeks companies with: A strong business franchise that offers growth potential. Products and services in which the company has a competitive advantage. A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company. The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down. Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives. Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility. Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies. Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors. Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.
Risk Lose Money [Text]	rr_RiskLoseMoney	There is no assurance that the Fund will achieve its investment objective and you may lose money.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities. The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares. The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800.345.6611
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	columbiathreadneedle.com/us
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Year by Year Total Return (%) as of December 31 Each Year
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best and Worst Quarterly Returns During the Period Shown in the Bar Chart Best                            3rd Quarter 2009                            23.55% Worst                         4th Quarter 2008                            -27.96%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs).
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	The after-tax returns are shown only for Class Z shares and will vary for other share classes.
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.
Columbia Acorn USA | Class A
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[1]
Management fees	rr_ManagementFeesOverAssets	0.86%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.23%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.34%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	704
3 years	rr_ExpenseExampleYear03	975
5 years	rr_ExpenseExampleYear05	1,267
10 years	rr_ExpenseExampleYear10	2,095
1 year	rr_ExpenseExampleNoRedemptionYear01	704
3 years	rr_ExpenseExampleNoRedemptionYear03	975
5 years	rr_ExpenseExampleNoRedemptionYear05	1,267
10 years	rr_ExpenseExampleNoRedemptionYear10	2,095
1 Year	rr_AverageAnnualReturnYear01	(2.58%)
5 Years	rr_AverageAnnualReturnYear05	12.23%
10 Years	rr_AverageAnnualReturnYear10	6.69%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn USA | Class B
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	5.00%	[2]
Management fees	rr_ManagementFeesOverAssets	0.86%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.75%
Other expenses	rr_OtherExpensesOverAssets	0.65%
Total annual Fund operating expenses	rr_ExpensesOverAssets	2.26%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge decreases over time.
1 year	rr_ExpenseExampleYear01	729
3 years	rr_ExpenseExampleYear03	1,006
5 years	rr_ExpenseExampleYear05	1,410
10 years	rr_ExpenseExampleYear10	2,363
1 year	rr_ExpenseExampleNoRedemptionYear01	229
3 years	rr_ExpenseExampleNoRedemptionYear03	706
5 years	rr_ExpenseExampleNoRedemptionYear05	1,210
10 years	rr_ExpenseExampleNoRedemptionYear10	2,363
1 Year	rr_AverageAnnualReturnYear01	(1.74%)
5 Years	rr_AverageAnnualReturnYear05	12.50%
10 Years	rr_AverageAnnualReturnYear10	6.59%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn USA | Class C
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[3]
Management fees	rr_ManagementFeesOverAssets	0.86%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.14%
Total annual Fund operating expenses	rr_ExpensesOverAssets	2.00%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge applies to redemptions within one year after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	303
3 years	rr_ExpenseExampleYear03	627
5 years	rr_ExpenseExampleYear05	1,078
10 years	rr_ExpenseExampleYear10	2,327
1 year	rr_ExpenseExampleNoRedemptionYear01	203
3 years	rr_ExpenseExampleNoRedemptionYear03	627
5 years	rr_ExpenseExampleNoRedemptionYear05	1,078
10 years	rr_ExpenseExampleNoRedemptionYear10	2,327
1 Year	rr_AverageAnnualReturnYear01	1.85%
5 Years	rr_AverageAnnualReturnYear05	12.76%
10 Years	rr_AverageAnnualReturnYear10	6.52%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn USA | Class I
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.86%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.08%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.94%
1 year	rr_ExpenseExampleYear01	96
3 years	rr_ExpenseExampleYear03	300
5 years	rr_ExpenseExampleYear05	520
10 years	rr_ExpenseExampleYear10	1,155
1 year	rr_ExpenseExampleNoRedemptionYear01	96
3 years	rr_ExpenseExampleNoRedemptionYear03	300
5 years	rr_ExpenseExampleNoRedemptionYear05	520
10 years	rr_ExpenseExampleNoRedemptionYear10	1,155
1 Year	rr_AverageAnnualReturnYear01	3.80%
5 Years	rr_AverageAnnualReturnYear05	14.00%
10 Years	rr_AverageAnnualReturnYear10	7.68%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 27, 2010
Columbia Acorn USA | Class R4
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.86%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.21%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.07%
1 year	rr_ExpenseExampleYear01	109
3 years	rr_ExpenseExampleYear03	340
5 years	rr_ExpenseExampleYear05	590
10 years	rr_ExpenseExampleYear10	1,306
1 year	rr_ExpenseExampleNoRedemptionYear01	109
3 years	rr_ExpenseExampleNoRedemptionYear03	340
5 years	rr_ExpenseExampleNoRedemptionYear05	590
10 years	rr_ExpenseExampleNoRedemptionYear10	1,306
1 Year	rr_AverageAnnualReturnYear01	3.60%
5 Years	rr_AverageAnnualReturnYear05	13.89%
10 Years	rr_AverageAnnualReturnYear10	7.63%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn USA | Class R5
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.86%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.13%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.99%
1 year	rr_ExpenseExampleYear01	101
3 years	rr_ExpenseExampleYear03	315
5 years	rr_ExpenseExampleYear05	547
10 years	rr_ExpenseExampleYear10	1,213
1 year	rr_ExpenseExampleNoRedemptionYear01	101
3 years	rr_ExpenseExampleNoRedemptionYear03	315
5 years	rr_ExpenseExampleNoRedemptionYear05	547
10 years	rr_ExpenseExampleNoRedemptionYear10	1,213
1 Year	rr_AverageAnnualReturnYear01	3.68%
5 Years	rr_AverageAnnualReturnYear05	13.91%
10 Years	rr_AverageAnnualReturnYear10	7.64%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn USA | Class Y
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.86%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.08%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.94%
1 year	rr_ExpenseExampleYear01	96
3 years	rr_ExpenseExampleYear03	300
5 years	rr_ExpenseExampleYear05	520
10 years	rr_ExpenseExampleYear10	1,155
1 year	rr_ExpenseExampleNoRedemptionYear01	96
3 years	rr_ExpenseExampleNoRedemptionYear03	300
5 years	rr_ExpenseExampleNoRedemptionYear05	520
10 years	rr_ExpenseExampleNoRedemptionYear10	1,155
1 Year	rr_AverageAnnualReturnYear01	3.76%
5 Years	rr_AverageAnnualReturnYear05	13.94%
10 Years	rr_AverageAnnualReturnYear10	7.65%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn USA | Class Z
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.86%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.22%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.08%
1 year	rr_ExpenseExampleYear01	110
3 years	rr_ExpenseExampleYear03	343
5 years	rr_ExpenseExampleYear05	595
10 years	rr_ExpenseExampleYear10	1,317
1 year	rr_ExpenseExampleNoRedemptionYear01	110
3 years	rr_ExpenseExampleNoRedemptionYear03	343
5 years	rr_ExpenseExampleNoRedemptionYear05	595
10 years	rr_ExpenseExampleNoRedemptionYear10	1,317
2005	rr_AnnualReturn2005	12.98%	[4]
2006	rr_AnnualReturn2006	8.28%	[4]
2007	rr_AnnualReturn2007	3.46%	[4]
2008	rr_AnnualReturn2008	(39.22%)	[4]
2009	rr_AnnualReturn2009	41.49%	[4]
2010	rr_AnnualReturn2010	23.16%	[4]
2011	rr_AnnualReturn2011	(4.95%)	[4]
2012	rr_AnnualReturn2012	18.98%	[4]
2013	rr_AnnualReturn2013	32.72%	[4]
2014	rr_AnnualReturn2014	3.61%	[4]
Year to Date Return, Label	rr_YearToDateReturnLabel	Year to Date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2015
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	5.12%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	23.55%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(27.96%)
1 Year	rr_AverageAnnualReturnYear01	3.61%
5 Years	rr_AverageAnnualReturnYear05	13.88%
10 Years	rr_AverageAnnualReturnYear10	7.62%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 04, 1996
Columbia Acorn USA | returns after taxes on distributions | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(0.52%)
5 Years	rr_AverageAnnualReturnYear05	12.21%
10 Years	rr_AverageAnnualReturnYear10	6.57%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 04, 1996
Columbia Acorn USA | returns after taxes on distributions and sale of Fund shares | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	5.33%
5 Years	rr_AverageAnnualReturnYear05	11.17%
10 Years	rr_AverageAnnualReturnYear10	6.22%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 04, 1996
Columbia Acorn USA | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	4.89%
5 Years	rr_AverageAnnualReturnYear05	15.55%
10 Years	rr_AverageAnnualReturnYear10	7.77%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge decreases over time.

[3] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[4] Year to Date return as of March 31, 2015: 5.12%

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2015
Columbia Acorn Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY OF THE FUND
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Columbia Acorn® Fund (the Fund) seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 21 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 17% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	17.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 21 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that: you invest $10,000 in the applicable class of Fund shares for the periods indicated, your investment has a 5% return each year, and the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $5 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $5 billion at the time of initial investment. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil). The Investment Manager typically seeks companies with: A strong business franchise that offers growth potential. Products and services in which the company has a competitive advantage. A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company. The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down. Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives. Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies. Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors. Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility. Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar. Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers. Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking. Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations. Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations. Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Liquidity and Trading Volume Risk. Because the Fund may invest a percentage of its assets in foreign securities, it may be subject to the liquidity and trading volume risks associated with international investing. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell foreign portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell these securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in foreign portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance. Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar. Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.
Risk Lose Money [Text]	rr_RiskLoseMoney	There is no assurance that the Fund will achieve its investment objective and you may lose money.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with those of the Russell 2500 Index, the Fund’s primary benchmark, the Russell 2000 Index and the Standard & Poor’s (S&P) 500® Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund’s performance compares to a widely recognized index of companies with somewhat lower capitalization than the Fund’s primary benchmark. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500® Index is presented to show performance against a widely recognized broad-based market index. The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities. The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares. The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with those of the Russell 2500 Index, the Fund’s primary benchmark, the Russell 2000 Index and the Standard & Poor’s (S&P) 500® Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund’s performance compares to a widely recognized index of companies with somewhat lower capitalization than the Fund’s primary benchmark. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500® Index is presented to show performance against a widely recognized broad-based market index.
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	The table below the bar chart compares the Fund’s returns for the periods shown with those of the Russell 2500 Index, the Fund’s primary benchmark, the Russell 2000 Index and the Standard & Poor’s (S&P) 500® Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund’s performance compares to a widely recognized index of companies with somewhat lower capitalization than the Fund’s primary benchmark. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500® Index is presented to show performance against a widely recognized broad-based market index.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800.345.6611
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	columbiathreadneedle.com/us
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Year by Year Total Return (%) as of December 31 Each Year
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best and Worst Quarterly Returns During the Period Shown in the Bar Chart Best                            2nd Quarter 2009                            20.90% Worst                         4th Quarter 2008                            -25.11%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs).
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	The after-tax returns are shown only for Class Z shares and will vary for other share classes.
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.
Columbia Acorn Fund | Class A
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[1]
Management fees	rr_ManagementFeesOverAssets	0.64%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.19%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.08%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	679
3 years	rr_ExpenseExampleYear03	899
5 years	rr_ExpenseExampleYear05	1,136
10 years	rr_ExpenseExampleYear10	1,816
1 year	rr_ExpenseExampleNoRedemptionYear01	679
3 years	rr_ExpenseExampleNoRedemptionYear03	899
5 years	rr_ExpenseExampleNoRedemptionYear05	1,136
10 years	rr_ExpenseExampleNoRedemptionYear10	1,816
1 Year	rr_AverageAnnualReturnYear01	(5.23%)
5 Years	rr_AverageAnnualReturnYear05	11.69%
10 Years	rr_AverageAnnualReturnYear10	7.44%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn Fund | Class B
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	5.00%	[2]
Management fees	rr_ManagementFeesOverAssets	0.64%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.75%
Other expenses	rr_OtherExpensesOverAssets	0.37%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.76%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge decreases over time.
1 year	rr_ExpenseExampleYear01	679
3 years	rr_ExpenseExampleYear03	854
5 years	rr_ExpenseExampleYear05	1,154
10 years	rr_ExpenseExampleYear10	1,894
1 year	rr_ExpenseExampleNoRedemptionYear01	179
3 years	rr_ExpenseExampleNoRedemptionYear03	554
5 years	rr_ExpenseExampleNoRedemptionYear05	954
10 years	rr_ExpenseExampleNoRedemptionYear10	1,894
1 Year	rr_AverageAnnualReturnYear01	(4.27%)
5 Years	rr_AverageAnnualReturnYear05	12.08%
10 Years	rr_AverageAnnualReturnYear10	7.41%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn Fund | Class C
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[3]
Management fees	rr_ManagementFeesOverAssets	0.64%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.14%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.78%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge applies to redemptions within one year after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	281
3 years	rr_ExpenseExampleYear03	560
5 years	rr_ExpenseExampleYear05	964
10 years	rr_ExpenseExampleYear10	2,095
1 year	rr_ExpenseExampleNoRedemptionYear01	181
3 years	rr_ExpenseExampleNoRedemptionYear03	560
5 years	rr_ExpenseExampleNoRedemptionYear05	964
10 years	rr_ExpenseExampleNoRedemptionYear10	2,095
1 Year	rr_AverageAnnualReturnYear01	(0.98%)
5 Years	rr_AverageAnnualReturnYear05	12.18%
10 Years	rr_AverageAnnualReturnYear10	7.25%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn Fund | Class I
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.64%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.07%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.71%
1 year	rr_ExpenseExampleYear01	73
3 years	rr_ExpenseExampleYear03	227
5 years	rr_ExpenseExampleYear05	395
10 years	rr_ExpenseExampleYear10	883
1 year	rr_ExpenseExampleNoRedemptionYear01	73
3 years	rr_ExpenseExampleNoRedemptionYear03	227
5 years	rr_ExpenseExampleNoRedemptionYear05	395
10 years	rr_ExpenseExampleNoRedemptionYear10	883
1 Year	rr_AverageAnnualReturnYear01	0.91%
5 Years	rr_AverageAnnualReturnYear05	13.41%
10 Years	rr_AverageAnnualReturnYear10	8.42%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 27, 2010
Columbia Acorn Fund | Class R4
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.64%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.20%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.84%
1 year	rr_ExpenseExampleYear01	86
3 years	rr_ExpenseExampleYear03	268
5 years	rr_ExpenseExampleYear05	466
10 years	rr_ExpenseExampleYear10	1,037
1 year	rr_ExpenseExampleNoRedemptionYear01	86
3 years	rr_ExpenseExampleNoRedemptionYear03	268
5 years	rr_ExpenseExampleNoRedemptionYear05	466
10 years	rr_ExpenseExampleNoRedemptionYear10	1,037
1 Year	rr_AverageAnnualReturnYear01	0.81%
5 Years	rr_AverageAnnualReturnYear05	13.33%
10 Years	rr_AverageAnnualReturnYear10	8.38%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn Fund | Class R5
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.64%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.12%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.76%
1 year	rr_ExpenseExampleYear01	78
3 years	rr_ExpenseExampleYear03	243
5 years	rr_ExpenseExampleYear05	422
10 years	rr_ExpenseExampleYear10	942
1 year	rr_ExpenseExampleNoRedemptionYear01	78
3 years	rr_ExpenseExampleNoRedemptionYear03	243
5 years	rr_ExpenseExampleNoRedemptionYear05	422
10 years	rr_ExpenseExampleNoRedemptionYear10	942
1 Year	rr_AverageAnnualReturnYear01	0.89%
5 Years	rr_AverageAnnualReturnYear05	13.37%
10 Years	rr_AverageAnnualReturnYear10	8.40%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn Fund | Class Y
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.64%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.07%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.71%
1 year	rr_ExpenseExampleYear01	73
3 years	rr_ExpenseExampleYear03	227
5 years	rr_ExpenseExampleYear05	395
10 years	rr_ExpenseExampleYear10	883
1 year	rr_ExpenseExampleNoRedemptionYear01	73
3 years	rr_ExpenseExampleNoRedemptionYear03	227
5 years	rr_ExpenseExampleNoRedemptionYear05	395
10 years	rr_ExpenseExampleNoRedemptionYear10	883
1 Year	rr_AverageAnnualReturnYear01	0.94%
5 Years	rr_AverageAnnualReturnYear05	13.39%
10 Years	rr_AverageAnnualReturnYear10	8.41%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn Fund | Class Z
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.64%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.15%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.79%
1 year	rr_ExpenseExampleYear01	81
3 years	rr_ExpenseExampleYear03	252
5 years	rr_ExpenseExampleYear05	439
10 years	rr_ExpenseExampleYear10	978
1 year	rr_ExpenseExampleNoRedemptionYear01	81
3 years	rr_ExpenseExampleNoRedemptionYear03	252
5 years	rr_ExpenseExampleNoRedemptionYear05	439
10 years	rr_ExpenseExampleNoRedemptionYear10	978
2005	rr_AnnualReturn2005	13.11%	[4]
2006	rr_AnnualReturn2006	14.45%	[4]
2007	rr_AnnualReturn2007	7.69%	[4]
2008	rr_AnnualReturn2008	(38.55%)	[4]
2009	rr_AnnualReturn2009	39.65%	[4]
2010	rr_AnnualReturn2010	26.00%	[4]
2011	rr_AnnualReturn2011	(4.61%)	[4]
2012	rr_AnnualReturn2012	17.93%	[4]
2013	rr_AnnualReturn2013	30.90%	[4]
2014	rr_AnnualReturn2014	0.82%	[4]
Year to Date Return, Label	rr_YearToDateReturnLabel	Year to Date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2015
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	3.97%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	20.90%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(25.11%)
1 Year	rr_AverageAnnualReturnYear01	0.82%
5 Years	rr_AverageAnnualReturnYear05	13.35%
10 Years	rr_AverageAnnualReturnYear10	8.39%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Jun. 10, 1970
Columbia Acorn Fund | returns after taxes on distributions | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(2.85%)
5 Years	rr_AverageAnnualReturnYear05	11.70%
10 Years	rr_AverageAnnualReturnYear10	7.21%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Jun. 10, 1970
Columbia Acorn Fund | returns after taxes on distributions and sale of Fund shares | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	3.43%
5 Years	rr_AverageAnnualReturnYear05	10.77%
10 Years	rr_AverageAnnualReturnYear10	6.90%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Jun. 10, 1970
Columbia Acorn Fund | Russell 2500 Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	7.07%
5 Years	rr_AverageAnnualReturnYear05	16.36%
10 Years	rr_AverageAnnualReturnYear10	8.72%
Columbia Acorn Fund | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	4.89%
5 Years	rr_AverageAnnualReturnYear05	15.55%
10 Years	rr_AverageAnnualReturnYear10	7.77%
Columbia Acorn Fund | S&P 500® Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	13.69%
5 Years	rr_AverageAnnualReturnYear05	15.45%
10 Years	rr_AverageAnnualReturnYear10	7.67%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge decreases over time.

[3] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[4] Year to Date return as of March 31, 2015: 3.97%

XML

Columbia Acorn USA

SUMMARY OF THE FUND

Investment Objective

Columbia Acorn USA^® (the Fund) seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 17 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Columbia Acorn USA	Class A		Class B		Class C		Class I	Class R4	Class R5	Class Y	Class Z
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%		none		none		none	none	none	none	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00%	[1]	5.00%	[2]	1.00%	[3]	none	none	none	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Columbia Acorn USA	Class A	Class B	Class C	Class I	Class R4	Class R5	Class Y	Class Z
Management fees	0.86%	0.86%	0.86%	0.86%	0.86%	0.86%	0.86%	0.86%
Distribution and/or service (12b-1) fees	0.25%	0.75%	1.00%	none	none	none	none	none
Other expenses	0.23%	0.65%	0.14%	0.08%	0.21%	0.13%	0.08%	0.22%
Total annual Fund operating expenses	1.34%	2.26%	2.00%	0.94%	1.07%	0.99%	0.94%	1.08%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in the applicable class of Fund shares for the periods indicated,

• your investment has a 5% return each year, and

• the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

Expense Example Columbia Acorn USA (USD $)	1 year	3 years	5 years	10 years
Class A	704	975	1,267	2,095
Class B	729	1,006	1,410	2,363
Class C	303	627	1,078	2,327
Class I	96	300	520	1,155
Class R4	109	340	590	1,306
Class R5	101	315	547	1,213
Class Y	96	300	520	1,155
Class Z	110	343	595	1,317

Expense Example, No Redemption Columbia Acorn USA (USD $)	1 year	3 years	5 years	10 years
Class A	704	975	1,267	2,095
Class B	229	706	1,210	2,363
Class C	203	627	1,078	2,327
Class I	96	300	520	1,155
Class R4	109	340	590	1,306
Class R5	101	315	547	1,213
Class Y	96	300	520	1,155
Class Z	110	343	595	1,317

Portfolio Turnover

The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 12% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (including the amount any borrowings for investment purposes) in U.S. companies.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $5 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $5 billion at the time of initial investment.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services in which the company has a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down.

Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives.

Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility.

Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies.

Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index.

The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities.

The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.

Year by Year Total Return (%)
as of December 31 Each Year

Best and Worst Quarterly Returns
During the Period Shown in the Bar Chart

Best                            3rd Quarter 2009                            23.55%

Worst                         4th Quarter 2008                            -27.96%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)

Average Annual Total Returns Columbia Acorn USA	Share Class Inception Date	1 Year	5 Years	10 Years
Class Z	Sep. 04, 1996	3.61%	13.88%	7.62%
Class Z returns after taxes on distributions	Sep. 04, 1996	(0.52%)	12.21%	6.57%
Class Z returns after taxes on distributions and sale of Fund shares	Sep. 04, 1996	5.33%	11.17%	6.22%
Class A	Oct. 16, 2000	(2.58%)	12.23%	6.69%
Class B	Oct. 16, 2000	(1.74%)	12.50%	6.59%
Class C	Oct. 16, 2000	1.85%	12.76%	6.52%
Class I	Sep. 27, 2010	3.80%	14.00%	7.68%
Class R4	Nov. 08, 2012	3.60%	13.89%	7.63%
Class R5	Nov. 08, 2012	3.68%	13.91%	7.64%
Class Y	Nov. 08, 2012	3.76%	13.94%	7.65%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)		4.89%	15.55%	7.77%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge decreases over time.

[3] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[1] Year to Date return as of March 31, 2015: 5.12%

XML

Columbia Acorn Select

SUMMARY OF THE FUND

Investment Objective

Columbia Acorn Select^SM (the Fund) seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 22 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Columbia Acorn Select	Class A		Class B		Class C		Class I	Class R4	Class R5	Class Y	Class Z
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%		none		none		none	none	none	none	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00%	[1]	5.00%	[2]	1.00%	[3]	none	none	none	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Columbia Acorn Select		Class A	Class B	Class C	Class I	Class R4	Class R5	Class Y	Class Z
Management fees		0.85%	0.85%	0.85%	0.85%	0.85%	0.85%	0.85%	0.85%
Distribution and/or service (12b-1) fees		0.25%	0.75%	1.00%	none	none	none	none	none
Other expenses		0.22%	0.55%	0.19%	0.10%	0.27%	0.15%	0.10%	0.19%
Total annual Fund operating expenses		1.32%	2.15%	2.04%	0.95%	1.12%	1.00%	0.95%	1.04%
Less: Fee waivers and/or expense reimbursements	[1]	(0.20%)	(0.20%)	(0.20%)	(0.20%)	(0.20%)	(0.20%)	(0.20%)	(0.20%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements		1.12%	1.95%	1.84%	0.75%	0.92%	0.80%	0.75%	0.84%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in the applicable class of Fund shares for the periods indicated,

• your investment has a 5% return each year, and

• the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first year of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

Expense Example Columbia Acorn Select (USD $)	1 year	3 years	5 years	10 years
Class A	683	951	1,239	2,057
Class B	698	954	1,336	2,256
Class C	287	620	1,080	2,353
Class I	77	283	506	1,148
Class R4	94	336	598	1,345
Class R5	82	298	533	1,206
Class Y	77	283	506	1,148
Class Z	86	311	555	1,253

Expense Example, No Redemption Columbia Acorn Select (USD $)	1 year	3 years	5 years	10 years
Class A	683	951	1,239	2,057
Class B	198	654	1,136	2,256
Class C	187	620	1,080	2,353
Class I	77	283	506	1,148
Class R4	94	336	598	1,345
Class R5	82	298	533	1,206
Class Y	77	283	506	1,148
Class Z	86	311	555	1,253

Portfolio Turnover

The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 17% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of companies with market capitalizations under $20 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $20 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $20 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $20 billion at the time of initial investment.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $20 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Colombia).

The Fund invests in a limited number of companies (generally between 30-60), offering the potential to provide above-average growth over time. In pursuit of the Fund’s objective, the portfolio managers may take advantage of the research and stock-picking capabilities of the Investment Manager to select investments that are “best ideas,” but need not do so and will generally concentrate the Fund’s investments in those sectors, companies, geographic regions or industries that the portfolio managers believe offer the most growth potential.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services in which the company has a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Fund may also invest in companies that the Investment Manager believes have good operational fundamentals but that the Investment Manager believes are undervalued due to negative investor sentiment related to company-specific or market-related conditions. Investments in turnaround and development stage companies may also be made when the Investment Manager believes potential returns outweigh risks of losses.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down.

Select Portfolio Risk. Because the Fund may invest in a limited number of companies, the Fund as a whole is subject to greater risk of loss if any of its portfolio securities decline in price. In addition, the Fund’s holdings and weightings will diverge significantly from its primary benchmark’s holdings and weightings and the Fund may therefore experience greater risk and volatility relative to the benchmark. Because the Fund may invest in more than one company concentrated in a similar industry, sector or geographic region, the Fund may be even more concentrated than the number of companies it may hold would suggest.

Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives.

Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility.

Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies.

Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors.

Opportunistic Investing Risk. Undervalued securities involve the risk that they may never reach their expected full market value, either because the market fails to recognize the security's intrinsic worth or the expected value was misgauged. Undervalued securities also may decline in price even though the Investment Manager believes they are already undervalued. Turnaround companies may never improve their fundamentals, may take much longer than expected to improve, or may improve much less than expected. Development stage companies could fail to develop and deplete their assets, resulting in large percentage losses.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.

Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations.

Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades.

Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations.

Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights.

Liquidity and Trading Volume Risk. Because the Fund may invest a percentage of its assets in foreign securities, it may be subject to the liquidity and trading volume risks associated with international investing. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell foreign portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell these securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in foreign portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance.

Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Standard & Poor’s (S&P) MidCap 400^® Index, the Fund’s primary benchmark, and the S&P 500^® Index. The S&P MidCap 400^® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500^® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500^® Index is presented to show performance against a widely recognized market index.

The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities.

The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.

Year by Year Total Return (%)
as of December 31 Each Year

Best and Worst Quarterly Returns
During the Period Shown in the Bar Chart

Best                            2nd Quarter 2009                            28.11%

Worst                         4th Quarter 2008                            -30.14%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)

Average Annual Total Returns Columbia Acorn Select	Share Class Inception Date	1 Year	5 Years	10 Years
Class Z	Nov. 23, 1998	2.47%	10.60%	7.33%
Class Z returns after taxes on distributions	Nov. 23, 1998	(2.20%)	7.98%	5.89%
Class Z returns after taxes on distributions and sale of Fund shares	Nov. 23, 1998	5.17%	8.33%	5.93%
Class A	Oct. 16, 2000	(3.70%)	8.98%	6.39%
Class B	Oct. 16, 2000	(2.60%)	9.30%	6.31%
Class C	Oct. 16, 2000	0.63%	9.45%	6.19%
Class I	Sep. 27, 2010	2.49%	10.69%	7.38%
Class R4	Nov. 08, 2012	2.39%	10.58%	7.32%
Class R5	Nov. 08, 2012	2.50%	10.62%	7.34%
Class Y	Nov. 08, 2012	2.53%	10.64%	7.35%
S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)		9.77%	16.54%	9.71%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)		13.69%	15.45%	7.67%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge decreases over time.

[3] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[1] Effective May 1, 2015, Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive 0.20% of the advisory fee otherwise payable to it by the Fund through April 30, 2016. This arrangement may only be modified or amended with approval from all parties to the arrangement, including the Fund and the Investment Manager.

[1] Year to Date return as of March 31, 2015: 2.83%

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2015
Columbia Acorn Emerging Markets Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY OF THE FUND
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Columbia Acorn Emerging Markets FundSM (the Fund) seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 24 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 45% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	45.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 24 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that: you invest $10,000 in the applicable class of Fund shares for the periods indicated, your investment has a 5% return each year, and the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in companies located in emerging market countries, including frontier market countries. Emerging market countries are those countries whose economies are developing or emerging from underdevelopment (for example, China, India, Poland and Turkey). Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries (for example, Vietnam, Colombia, Nigeria and Kazakhstan). For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, an emerging market country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in an emerging market country or countries or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector. Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $5 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $5 billion at the time of initial investment. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time. Generally, the Investment Manager will determine which countries are emerging market countries by reference to the countries included in the S&P Emerging Markets Broad Market® Index (BMI), and will determine which countries are frontier market countries by reference to the countries included in the S&P Frontier® BMI. In addition, the Fund may invest in certain developing market countries that are not included in either the S&P Emerging Markets® BMI or the S&P Frontier® BMI (for example, Serbia and Senegal), but which are included on another independent third-party listing of emerging market and/or frontier market countries. The Investment Manager will make all determinations as to whether a company is an emerging market company at the time of investment. The countries that comprise emerging market countries, including frontier market countries, may change from time to time. The Investment Manager typically seeks companies with: A strong business franchise that offers growth potential. Products and services in which the company has a competitive advantage. A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company. The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down. Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives. Liquidity and Trading Volume Risk. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance. Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar. Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers. Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking. Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations. Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations. Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Frontier Market Risk. Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries (which themselves have increased investment risk relative to more developed market countries) and, as a result, the Fund’s exposure to the risks associated with investing in emerging market countries are magnified when the Fund invests in frontier market countries. Increased risks include: the potential for extreme price volatility and illiquidity in frontier market countries; government ownership or control of parts of the private sector and of certain companies; trade barriers, exchange controls, managed adjustments in relative currency values and other protectionist and similar measures imposed or negotiated by the countries with which frontier market countries trade; and the relatively new and unsettled securities laws in many frontier market countries. Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar. Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies. Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility. Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors. Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility. Special Situations Risk. Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, may be exposed to heightened risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Certain “special situation” investments are investments in securities or other instruments that are determined to be illiquid or lacking a readily ascertainable fair value. Certain special situation investments prevent ownership interests therein from being withdrawn until the special situation investment, or a portion thereof, is realized or deemed realized, which may negatively impact Fund performance. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.
Risk Lose Money [Text]	rr_RiskLoseMoney	There is no assurance that the Fund will achieve its investment objective and you may lose money.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Standard & Poor’s (S&P) Emerging Markets Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, and the MSCI Emerging Markets Small Cap Index (Net). The S&P Emerging Markets Between $500 Million and $5 Billion® Index is representative of the institutionally investable capital of 20 emerging market countries (as of December 31, 2014), as determined by S&P, with market caps ranging between $500 million to $5 billion. The MSCI Emerging Markets Small Cap Index (Net) is a widely recognized international benchmark, and a free floating-adjusted market capitalization index that is designed to measure small-cap emerging market equity performance in 23 emerging market countries (as of December 31, 2014), as determined by MSCI. The performance of the MSCI Emerging Markets Small Cap Index (Net) is provided to show how the Fund's performance compares to a widely recognized index of small-capitalization equity performance in less developed markets. The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities. The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares. The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Standard & Poor’s (S&P) Emerging Markets Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, and the MSCI Emerging Markets Small Cap Index (Net). The S&P Emerging Markets Between $500 Million and $5 Billion® Index is representative of the institutionally investable capital of 20 emerging market countries (as of December 31, 2014), as determined by S&P, with market caps ranging between $500 million to $5 billion. The MSCI Emerging Markets Small Cap Index (Net) is a widely recognized international benchmark, and a free floating-adjusted market capitalization index that is designed to measure small-cap emerging market equity performance in 23 emerging market countries (as of December 31, 2014), as determined by MSCI. The performance of the MSCI Emerging Markets Small Cap Index (Net) is provided to show how the Fund's performance compares to a widely recognized index of small-capitalization equity performance in less developed markets.
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	The table below the bar chart compares the Fund’s returns for the periods shown with the Standard & Poor’s (S&P) Emerging Markets Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, and the MSCI Emerging Markets Small Cap Index (Net). The S&P Emerging Markets Between $500 Million and $5 Billion® Index is representative of the institutionally investable capital of 20 emerging market countries (as of December 31, 2014), as determined by S&P, with market caps ranging between $500 million to $5 billion. The MSCI Emerging Markets Small Cap Index (Net) is a widely recognized international benchmark, and a free floating-adjusted market capitalization index that is designed to measure small-cap emerging market equity performance in 23 emerging market countries (as of December 31, 2014), as determined by MSCI. The performance of the MSCI Emerging Markets Small Cap Index (Net) is provided to show how the Fund's performance compares to a widely recognized index of small-capitalization equity performance in less developed markets.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800.345.6611
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	columbiathreadneedle.com/us
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Year by Year Total Return (%) as of December 31 Each Year
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best and Worst Quarterly Returns During the Period Shown in the Bar Chart Best                            1st Quarter 2012                             18.00% Worst                         2nd Quarter 2012                            -6.90%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs).
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	The after-tax returns are shown only for Class Z shares and will vary for other share classes.
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.
Columbia Acorn Emerging Markets Fund | Class A
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[1]
Management fees	rr_ManagementFeesOverAssets	1.04%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.28%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.57%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	726
3 years	rr_ExpenseExampleYear03	1,042
5 years	rr_ExpenseExampleYear05	1,381
10 years	rr_ExpenseExampleYear10	2,335
1 year	rr_ExpenseExampleNoRedemptionYear01	726
3 years	rr_ExpenseExampleNoRedemptionYear03	1,042
5 years	rr_ExpenseExampleNoRedemptionYear05	1,381
10 years	rr_ExpenseExampleNoRedemptionYear10	2,335
1 Year	rr_AverageAnnualReturnYear01	(9.81%)
Life of Fund	rr_AverageAnnualReturnSinceInception	6.12%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 19, 2011
Columbia Acorn Emerging Markets Fund | Class C
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[2]
Management fees	rr_ManagementFeesOverAssets	1.04%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.29%
Total annual Fund operating expenses	rr_ExpensesOverAssets	2.33%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge applies to redemptions within one year after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	336
3 years	rr_ExpenseExampleYear03	727
5 years	rr_ExpenseExampleYear05	1,245
10 years	rr_ExpenseExampleYear10	2,666
1 year	rr_ExpenseExampleNoRedemptionYear01	236
3 years	rr_ExpenseExampleNoRedemptionYear03	727
5 years	rr_ExpenseExampleNoRedemptionYear05	1,245
10 years	rr_ExpenseExampleNoRedemptionYear10	2,666
1 Year	rr_AverageAnnualReturnYear01	(5.98%)
Life of Fund	rr_AverageAnnualReturnSinceInception	7.22%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 19, 2011
Columbia Acorn Emerging Markets Fund | Class I
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	1.04%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.17%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.21%
1 year	rr_ExpenseExampleYear01	123
3 years	rr_ExpenseExampleYear03	384
5 years	rr_ExpenseExampleYear05	665
10 years	rr_ExpenseExampleYear10	1,466
1 year	rr_ExpenseExampleNoRedemptionYear01	123
3 years	rr_ExpenseExampleNoRedemptionYear03	384
5 years	rr_ExpenseExampleNoRedemptionYear05	665
10 years	rr_ExpenseExampleNoRedemptionYear10	1,466
1 Year	rr_AverageAnnualReturnYear01	(4.01%)
Life of Fund	rr_AverageAnnualReturnSinceInception	8.42%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 19, 2011
Columbia Acorn Emerging Markets Fund | Class R4
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	1.04%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.24%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.28%
1 year	rr_ExpenseExampleYear01	130
3 years	rr_ExpenseExampleYear03	406
5 years	rr_ExpenseExampleYear05	702
10 years	rr_ExpenseExampleYear10	1,545
1 year	rr_ExpenseExampleNoRedemptionYear01	130
3 years	rr_ExpenseExampleNoRedemptionYear03	406
5 years	rr_ExpenseExampleNoRedemptionYear05	702
10 years	rr_ExpenseExampleNoRedemptionYear10	1,545
1 Year	rr_AverageAnnualReturnYear01	(4.03%)
Life of Fund	rr_AverageAnnualReturnSinceInception	8.38%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn Emerging Markets Fund | Class R5
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	1.04%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.22%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.26%
1 year	rr_ExpenseExampleYear01	128
3 years	rr_ExpenseExampleYear03	400
5 years	rr_ExpenseExampleYear05	692
10 years	rr_ExpenseExampleYear10	1,523
1 year	rr_ExpenseExampleNoRedemptionYear01	128
3 years	rr_ExpenseExampleNoRedemptionYear03	400
5 years	rr_ExpenseExampleNoRedemptionYear05	692
10 years	rr_ExpenseExampleNoRedemptionYear10	1,523
1 Year	rr_AverageAnnualReturnYear01	(4.02%)
Life of Fund	rr_AverageAnnualReturnSinceInception	8.39%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn Emerging Markets Fund | Class Y
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	1.04%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.17%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.21%
1 year	rr_ExpenseExampleYear01	123
3 years	rr_ExpenseExampleYear03	384
5 years	rr_ExpenseExampleYear05	665
10 years	rr_ExpenseExampleYear10	1,466
1 year	rr_ExpenseExampleNoRedemptionYear01	123
3 years	rr_ExpenseExampleNoRedemptionYear03	384
5 years	rr_ExpenseExampleNoRedemptionYear05	665
10 years	rr_ExpenseExampleNoRedemptionYear10	1,466
1 Year	rr_AverageAnnualReturnYear01	(3.95%)
Life of Fund	rr_AverageAnnualReturnSinceInception	8.40%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Jun. 13, 2013
Columbia Acorn Emerging Markets Fund | Class Z
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	1.04%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.29%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.33%
1 year	rr_ExpenseExampleYear01	135
3 years	rr_ExpenseExampleYear03	421
5 years	rr_ExpenseExampleYear05	729
10 years	rr_ExpenseExampleYear10	1,601
1 year	rr_ExpenseExampleNoRedemptionYear01	135
3 years	rr_ExpenseExampleNoRedemptionYear03	421
5 years	rr_ExpenseExampleNoRedemptionYear05	729
10 years	rr_ExpenseExampleNoRedemptionYear10	1,601
2012	rr_AnnualReturn2012	31.35%	[3]
2013	rr_AnnualReturn2013	11.92%	[3]
2014	rr_AnnualReturn2014	(4.12%)	[3]
Year to Date Return, Label	rr_YearToDateReturnLabel	Year to Date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2015
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	(0.78%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2012
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	18.00%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Jun. 30, 2012
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(6.90%)
1 Year	rr_AverageAnnualReturnYear01	(4.12%)
Life of Fund	rr_AverageAnnualReturnSinceInception	8.29%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 19, 2011
Columbia Acorn Emerging Markets Fund | returns after taxes on distributions | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(4.16%)
Life of Fund	rr_AverageAnnualReturnSinceInception	8.20%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 19, 2011
Columbia Acorn Emerging Markets Fund | returns after taxes on distributions and sale of Fund shares | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(2.02%)
Life of Fund	rr_AverageAnnualReturnSinceInception	6.56%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 19, 2011
Columbia Acorn Emerging Markets Fund | S&P Emerging Markets Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	1.90%
Life of Fund	rr_AverageAnnualReturnSinceInception	3.31%
Columbia Acorn Emerging Markets Fund | MSCI Emerging Markets Small Cap Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	1.01%
Life of Fund	rr_AverageAnnualReturnSinceInception	1.16%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[3] Year to Date return as of March 31, 2015: -0.78%

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Columbia Acorn Emerging Markets Fund

SUMMARY OF THE FUND

Investment Objective

Columbia Acorn Emerging Markets Fund^SM (the Fund) seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 24 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Columbia Acorn Emerging Markets Fund	Class A		Class C		Class I	Class R4	Class R5	Class Y	Class Z
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%		none		none	none	none	none	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00%	[1]	1.00%	[2]	none	none	none	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Columbia Acorn Emerging Markets Fund	Class A	Class C	Class I	Class R4	Class R5	Class Y	Class Z
Management fees	1.04%	1.04%	1.04%	1.04%	1.04%	1.04%	1.04%
Distribution and/or service (12b-1) fees	0.25%	1.00%	none	none	none	none	none
Other expenses	0.28%	0.29%	0.17%	0.24%	0.22%	0.17%	0.29%
Total annual Fund operating expenses	1.57%	2.33%	1.21%	1.28%	1.26%	1.21%	1.33%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in the applicable class of Fund shares for the periods indicated,

• your investment has a 5% return each year, and

• the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

Expense Example Columbia Acorn Emerging Markets Fund (USD $)	1 year	3 years	5 years	10 years
Class A	726	1,042	1,381	2,335
Class C	336	727	1,245	2,666
Class I	123	384	665	1,466
Class R4	130	406	702	1,545
Class R5	128	400	692	1,523
Class Y	123	384	665	1,466
Class Z	135	421	729	1,601

Expense Example, No Redemption Columbia Acorn Emerging Markets Fund (USD $)	1 year	3 years	5 years	10 years
Class A	726	1,042	1,381	2,335
Class C	236	727	1,245	2,666
Class I	123	384	665	1,466
Class R4	130	406	702	1,545
Class R5	128	400	692	1,523
Class Y	123	384	665	1,466
Class Z	135	421	729	1,601

Portfolio Turnover

The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 45% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in companies located in emerging market countries, including frontier market countries. Emerging market countries are those countries whose economies are developing or emerging from underdevelopment (for example, China, India, Poland and Turkey). Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries (for example, Vietnam, Colombia, Nigeria and Kazakhstan). For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, an emerging market country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in an emerging market country or countries or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $5 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $5 billion at the time of initial investment.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

Generally, the Investment Manager will determine which countries are emerging market countries by reference to the countries included in the S&P Emerging Markets Broad Market^® Index (BMI), and will determine which countries are frontier market countries by reference to the countries included in the S&P Frontier^® BMI. In addition, the Fund may invest in certain developing market countries that are not included in either the S&P Emerging Markets^® BMI or the S&P Frontier^® BMI (for example, Serbia and Senegal), but which are included on another independent third-party listing of emerging market and/or frontier market countries. The Investment Manager will make all determinations as to whether a company is an emerging market company at the time of investment. The countries that comprise emerging market countries, including frontier market countries, may change from time to time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services in which the company has a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down.

Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives.

Liquidity and Trading Volume Risk. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance.

Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations.

Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades.

Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations.

Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights.

Frontier Market Risk. Frontier market countries generally have smaller economies and even less developed capital markets than traditional emerging market countries (which themselves have increased investment risk relative to more developed market countries) and, as a result, the Fund’s exposure to the risks associated with investing in emerging market countries are magnified when the Fund invests in frontier market countries. Increased risks include: the potential for extreme price volatility and illiquidity in frontier market countries; government ownership or control of parts of the private sector and of certain companies; trade barriers, exchange controls, managed adjustments in relative currency values and other protectionist and similar measures imposed or negotiated by the countries with which frontier market countries trade; and the relatively new and unsettled securities laws in many frontier market countries.

Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.

Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors.

Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility.

Special Situations Risk. Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, may be exposed to heightened risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Certain “special situation” investments are investments in securities or other instruments that are determined to be illiquid or lacking a readily ascertainable fair value. Certain special situation investments prevent ownership interests therein from being withdrawn until the special situation investment, or a portion thereof, is realized or deemed realized, which may negatively impact Fund performance. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Standard & Poor’s (S&P) Emerging Markets Between $500 Million and $5 Billion^® Index, the Fund's primary benchmark, and the MSCI Emerging Markets Small Cap Index (Net). The S&P Emerging Markets Between $500 Million and $5 Billion^® Index is representative of the institutionally investable capital of 20 emerging market countries (as of December 31, 2014), as determined by S&P, with market caps ranging between $500 million to $5 billion. The MSCI Emerging Markets Small Cap Index (Net) is a widely recognized international benchmark, and a free floating-adjusted market capitalization index that is designed to measure small-cap emerging market equity performance in 23 emerging market countries (as of December 31, 2014), as determined by MSCI. The performance of the MSCI Emerging Markets Small Cap Index (Net) is provided to show how the Fund's performance compares to a widely recognized index of small-capitalization equity performance in less developed markets.

The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities.

The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.

Year by Year Total Return (%)
as of December 31 Each Year

Best and Worst Quarterly Returns
During the Period Shown in the Bar Chart

Best                            1st Quarter 2012                             18.00%

Worst                         2nd Quarter 2012                            -6.90%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)

Average Annual Total Returns Columbia Acorn Emerging Markets Fund	Share Class Inception Date	1 Year	Life of Fund
Class Z	Aug. 19, 2011	(4.12%)	8.29%
Class Z returns after taxes on distributions	Aug. 19, 2011	(4.16%)	8.20%
Class Z returns after taxes on distributions and sale of Fund shares	Aug. 19, 2011	(2.02%)	6.56%
Class A	Aug. 19, 2011	(9.81%)	6.12%
Class C	Aug. 19, 2011	(5.98%)	7.22%
Class I	Aug. 19, 2011	(4.01%)	8.42%
Class R4	Nov. 08, 2012	(4.03%)	8.38%
Class R5	Nov. 08, 2012	(4.02%)	8.39%
Class Y	Jun. 13, 2013	(3.95%)	8.40%
S&P Emerging Markets Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)		1.90%	3.31%
MSCI Emerging Markets Small Cap Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)		1.01%	1.16%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[1] Year to Date return as of March 31, 2015: -0.78%

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Label

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Value

Risk/Return:

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Registrant Name

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COLUMBIA ACORN TRUST

Prospectus Date

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May 01, 2015

Columbia Thermostat Fund

Risk/Return:

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Risk/Return [Heading]

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SUMMARY OF THE FUND

Objective [Heading]

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Investment Objective

Objective, Primary [Text Block]

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Columbia Thermostat Fund^SM (the Fund) seeks long-term capital appreciation.

Expense [Heading]

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Fees and Expenses of the Fund

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 40 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.

Shareholder Fees Caption [Text]

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Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

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Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

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April 30, 2016

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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The Fund will indirectly bear the expenses associated with portfolio turnover of the underlying Portfolio Funds in which the Fund invests. Each Portfolio Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A Portfolio Fund’s higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when its shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 95% of the average value of its portfolio.

Portfolio Turnover, Rate

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95.00%

Expense Breakpoint Discounts [Text]

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You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 40 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.

Expense Breakpoint, Minimum Investment Required [Amount]

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50,000

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

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“Total annual Fund operating expenses” include acquired fund (Portfolio Fund) fees and expenses (expenses the Fund incurs indirectly through its investments in other funds) and may be higher than “Total Net Expenses” shown in the Financial Highlights section of this prospectus because “Total Net Expenses” do not include Portfolio Fund (acquired fund) fees and expenses.

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in the applicable class of Fund shares for the periods indicated,

• your investment has a 5% return each year, and

• the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first year of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

Strategy [Heading]

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Principal Investment Strategies

Strategy Narrative [Text Block]

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The Fund is primarily managed as a fund that invests in other funds (i.e., a “fund-of-funds”) that seeks to achieve its investment objective by investing its assets among a selected group of underlying stock and bond mutual funds for which Columbia Wanger Asset Management, LLC, the Fund’s investment adviser (the Investment Manager) or its affiliates, including Columbia Management Investment Advisers, LLC, serves as investment adviser or principal underwriter (the Portfolio Funds). Under normal circumstances, the Fund allocates at least 95% of its net assets (stock/bond assets) among the Portfolio Funds according to the current level of Standard & Poor’s (S&P) 500^® Index. Generally, when the S&P 500^® Index goes up in relation to predetermined ranges set by the Investment Manager, the Fund sells a portion of its stock funds and invests more in the bond funds and when the S&P 500^® Index goes down in relation to the ranges, the Fund increases its investment in the stock funds. Under normal circumstances, the Fund may invest up to 5% of net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Many asset allocation funds typically move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for the Fund are made according to a single predetermined rule. The temperature in your house is run by a single rule: your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Columbia Thermostat Fund.

Because the Fund invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than the Fund, the Fund is designed for those who doubt the wisdom of trying to “time” the market and are unsure of the long-term trend of the stock market. The Fund takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. The Fund operates continuously and substantially automatically, subject to periodic review of the pre-set program by the Investment Manager and the Fund’s Board of Trustees. As described more fully below, the Investment Manager has the authority to review the structure and allocation ranges of the stock/bond allocation table and to make any changes considered appropriate.

The Investment Manager chooses the Portfolio Funds to provide participation in the major sectors of the stock market and the portions of the bond market it believes will preserve capital and generate returns. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did not make significant new highs. The Fund may be a good investment choice for you if you believe that the market will fluctuate significantly and provide modest to no secular growth for many years.

The Fund invests its stock/bond assets among the Portfolio Funds according to an asset allocation table. The Investment Manager calibrates the allocation table such that stock percentages vary inversely with price-to-earnings ratios on “normalized” (long-term) earnings. Within a range of 10% to 90%, stock percentages rise towards maximum allocations as such price-to-earnings ratios fall towards historical lows, and stock percentages fall as such price-to-earnings ratios rise towards historical highs.

The Fund’s current allocation table is set forth below.

Stock/Bond Allocation Table
	How the Fund will Invest the Stock/Bond Assets
Level of the S&P 500® Index	Stock Percentage	Bond Percentage
over 2225	10%	90%
over 2150 – 2225	15%	85%
over 2075 – 2150	20%	80%
over 2000 – 2075	25%	75%
over 1925 – 2000	30%	70%
over 1850 – 1925	35%	65%
over 1775 – 1850	40%	60%
over 1700 – 1775	45%	55%
over 1625 – 1700	50%	50%
over 1550 – 1625	55%	45%
over 1475 – 1550	60%	40%
over 1400 – 1475	65%	35%
over 1325 – 1400	70%	30%
over 1250 – 1325	75%	25%
over 1175 – 1250	80%	20%
over 1100 – 1175	85%	15%
1100 and under	90%	10%

When the S&P 500^® Index moves into a new band on the table, the Fund will rebalance the stock/bond mix to reflect the new S&P 500^® Index price level by redeeming shares of some Portfolio Funds and purchasing shares of other Portfolio Funds. Any such rebalancing typically will be implemented promptly. However, there are two circumstances when a rebalancing may be implemented over a longer timeline. First, when a rebalancing or allocation table change would trigger a 10% point or greater change in stock and bond allocations or individual Portfolio Funds, the rebalancing may be implemented over a period of up to two weeks, if deemed by the Investment Manager to be in the best interest of shareholders. The second exception is a “31-day Rule;” in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock/bond mix, if the S&P 500^® Index remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. The Investment Manager will invest cash flows from sales (or redemptions) of Fund shares to bring the stock/bond mix back toward the allocation percentages for that S&P 500^® Index band. For example, if the S&P 500^® Index is in the 1150-1200 band, and the value of the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, the Investment Manager would invest new cash in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds). If the 31-day Rule is in effect, the Investment Manager will invest new cash at the stock/bond percentage allocation as of the latest rebalancing.

As an illustrative example, suppose the following:

Date	Level of the S&P 500® Index	How the Fund will invest the Stock/ Bond Assets
Nov. 1	We begin when the market is 1680	50% stocks, 50% bonds
Dec. 1	The S&P 500® goes to 1701	rebalance 45% stocks, 55% bonds
Dec. 6	The S&P 500® drops back to 1690	no reversal for 31 days
Jan. 2	The S&P 500® is at 1650	rebalance 50% stocks, 50% bonds
Jan. 20	The S&P 500® drops to 1620	rebalance 55% stocks, 45% bonds
	The market has made a continuation move by going through a second action level, not a reversal move, so the 31-day Rule does not apply in this case.
Jan. 30	The S&P 500® goes up to 1630	no reversal for 31 days
Feb. 20	The S&P 500® is at 1640	rebalance 50% stocks, 50% bonds

The following table shows the seven stock Portfolio Funds and four bond Portfolio Funds that the Fund currently uses in its “fund-of-funds” structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. As described more fully below, the Investment Manager may substitute or add additional Portfolio Funds at any time, including funds introduced after the date of this prospectus. The allocation percentage within each stock/bond category is achieved by rebalancing the investments within the category whenever the S&P 500^® Index moves into a new band on the allocation table, subject to the 31-day Rule described above. The Fund does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500^® Index into a new band (or due to a change by the Investment Manager in the stock/bond allocation table to the Portfolio Funds or to the relative allocation among them). Until a subsequent rebalancing, the Fund's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among the Portfolio Funds in a manner that will reduce any deviation of the relative values of the Fund's holdings of the Funds from the allocation percentages shown below.

Allocation of Stock/Bond Asset Within Asset Classes
	Type of Fund	Allocation
Stock Funds
Columbia Acorn® Fund	Small/Mid-cap growth	10%
Columbia Acorn International®	Small/Mid-cap international growth	20%
Columbia Acorn SelectSM	Mid-cap growth	10%
Columbia Contrarian Core Fund	Large-cap blend	20%
Columbia Dividend Income Fund	Large-cap value	20%
Columbia Large Cap Enhanced Core Fund	Large-cap blend	10%
Columbia Select Large Cap Growth Fund	Large-cap growth	10%
Total		100%
Bond Funds	Type of Fund	Allocation
Columbia Income Opportunities Fund	High-yield bond	20%
Columbia Intermediate Bond Fund	Intermediate-term bond	20%
Columbia Short Term Bond Fund	Short term bond	40%
Columbia U.S. Government Mortgage Fund	Government bond	20%
Total		100%

See the Portfolio Funds Summary section of this prospectus for information about the Portfolio Funds’ investment objectives and principal investment strategies.

The Investment Manager has the authority to review the Portfolio Funds and the relative stock/bond allocation percentages among them and to make any changes considered appropriate.

Each of the Portfolio Funds is currently managed by the Investment Manager or its affiliates. The Fund does not pay any sales load on its purchases of shares of the Portfolio Funds. On an annual basis, or on an “emergency” basis if necessary, the Investment Manager reviews the structure, allocation percentages and Portfolio Funds and makes any changes considered appropriate. The Investment Manager typically addresses the following questions:

• Should the stock/bond allocation table be revised (perhaps because the stock market has made a long-term move outside of the bands set forth above)?

• Should there be a change in the Portfolio Funds or should there be a change in the percentage allocations among the stock/bond funds (perhaps because of a change of portfolio managers, change of investment style, change in relative valuation or a reorganization of a Portfolio Fund)?

Any such changes by the Investment Manager are expected to be infrequent.

Risk [Heading]

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Principal Risks

Risk Narrative [Text Block]

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An investment in the Fund involves risk, including general risks relating to the investment in the Fund based on its investment process and its "fund-of-funds" structure, as well as specific risks related to the individual Portfolio Funds, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down.

Allocation Risk. The Investment Manager uses an asset allocation strategy in pursuing the Fund’s investment objective. There is a risk that the Fund's allocation among asset classes or investments will cause the Fund's shares to lose value or cause the Fund to underperform other funds with similar investment objectives and/or strategies, or that the investments themselves will not produce the returns expected.

Fund-of-Funds Risk. Determinations regarding asset classes or underlying funds and the Fund’s allocations thereto may not successfully achieve the Fund’s investment objective, in whole or in part. The ability of the Fund to realize its investment objective will depend, in large part, on the extent to which the underlying funds realize their investment objective. There is no guarantee that the underlying funds will achieve their respective investment objectives. The Fund is exposed to the same risks as the underlying funds in direct proportion to the allocation of its assets among the underlying funds. By investing in a combination of underlying funds, the Fund has exposure to the risks of many areas of the market. The performance of underlying funds could be adversely affected if other entities that invest in the same underlying funds make relatively large investments or redemptions in such underlying funds. The Fund, and its shareholders, indirectly bear a portion of the expenses of any funds in which the Fund invests. Because the expenses and costs of each underlying fund are shared by its investors, redemptions by other investors in an underlying fund could result in decreased economies of scale and increased operating expenses for such fund. The Investment Manager may have potential conflicts of interest in selecting affiliated funds over unaffiliated funds for investment by the Fund, and may also face potential conflicts of interest in selecting affiliated funds, because the fees the Investment Manager receives from some underlying funds may be higher than the fees paid by other underlying funds. Further, because of the Investment Manager’s confidence in its own strategies, investment philosophy and capacities, it will, in selecting underlying funds, at times prefer a fund in the Columbia Acorn Family of Funds over alternative investments. There can be no assurance, however, that a fund in the Columbia Acorn Family of Funds selected for inclusion in Columbia Thermostat Fund’s portfolio will, in fact, outperform similar funds managed by the Investment Manager’s affiliates.

The Fund is subject indirectly to the following risks of the Portfolio Funds:

Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility.

Interest Rate Risk. Interest rate risk is the risk of losses attributable to changes in interest rates. In general, if prevailing interest rates rise, the values of debt securities tend to fall, and if interest rates fall, the values of debt securities tend to rise. Changes in the value of a debt security usually will not affect the amount of income the Fund receives from it but will usually affect the value of the Fund's shares. In general, the longer the maturity or duration of a debt security, the greater its sensitivity to changes in interest rates. Interest rate declines also may increase prepayments of debt obligations, which, in turn, would increase prepayment risk. Similarly, a period of rising interest rates may negatively impact the Fund’s performance. Actions by governments and central banking authorities can result in increases in interest rates. Such actions may negatively affect the value of fixed-income securities held by the Fund, resulting in a negative impact on the Fund's performance and NAV. Securities with floating interest rates are typically less sensitive to interest rate changes, but may decline in value if their interest rates do not rise as much as interest rates in general. Because rates on certain floating rate loans and other debt securities reset only periodically, changes in prevailing interest rates (and particularly sudden and significant changes) can be expected to cause fluctuations in the Fund’s NAV.

Credit Risk. The value of fixed-income securities, or other instruments or assets, may decline if the issuer thereof defaults or otherwise becomes unable or unwilling, or is perceived to be unable or unwilling, to honor its financial obligations, such as making payments to the Fund when due. Rating agencies assign credit ratings to certain fixed-income securities to indicate their credit risk. Lower quality or unrated securities held by the Fund may present increased credit risk as compared to higher-rated securities. Non-investment grade fixed-income securities (commonly called “high-yield” or “junk”) are subject to greater price fluctuations and are more likely to experience a default than investment grade securities and therefore may expose the Fund to increased credit risk. If the Fund purchases unrated securities, or if the ratings of securities held by the Fund are lowered after purchase, the Fund will depend on analysis of credit risk more heavily than usual.

High-Yield Securities Risk. Securities rated below investment grade (commonly called “high-yield” or “junk” bonds) and unrated securities of comparable quality expose the Fund to a greater risk of loss of principal and income than a fund that invests solely or primarily in investment grade securities. In addition, these investments have greater price fluctuations, are less liquid and are more likely to experience a default than higher-rated securities. High-yield securities are considered to be predominantly speculative with respect to the issuer’s capacity to pay interest and repay principal.

Value Securities Risk. Value securities are securities of companies that may have experienced, for example, adverse business, industry or other developments or may be subject to special risks that have caused the securities to be out of favor and, in turn, potentially undervalued. The market value of a portfolio security may not meet the Investment Manager’s perceived value assessment of that security, or may decline in price, even though the Investment Manager believes the securities are already undervalued. There is also a risk that it may take longer than expected for the value of these investments to rise to the portfolio manager’s perceived value. In addition, value securities, at times, may not perform as well as growth securities or the stock market in general, and may be out of favor with investors for varying periods of time.

Growth Securities Risk. Growth securities typically trade at a higher multiple of earnings than other types of equity securities. Accordingly, the market values of growth securities may never reach their expected market value and may decline in price. In addition, growth securities, at times, may not perform as well as value securities or the stock market in general, and may be out of favor with investors for varying periods of time.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.

Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations.

Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades.

Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations.

Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights.

Liquidity and Trading Volume Risk. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance.

Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies.

U.S. Government Obligations Risk. While U.S. Treasury obligations are backed by the “full faith and credit” of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government.

Derivatives Risk. Losses involving derivative instruments may be substantial, because a relatively small movement in the price of an underlying security, instrument, commodity, currency or index may result in a substantial loss for the Fund. In addition to the potential for increased losses, the use of derivative instruments may lead to increased volatility for the Fund. Derivative investments will typically increase the Fund’s exposure to principal risks to which it is otherwise exposed, and may expose the Fund to additional risks, including correlation risk, counterparty risk, hedging risk, leverage risk and/or liquidity risk.

Convertible Securities Risk. Convertible securities are subject to the usual risks associated with debt securities, such as interest rate risk and credit risk. Convertible securities also react to changes in the value of the common stock into which they convert, and are thus subject to market risk. The Fund may also be forced to convert a convertible security at an inopportune time, which may decrease the Fund’s return.

Forward Commitments on Mortgage-Backed Securities (including Dollar Rolls) Risk. When purchasing mortgage-backed securities in the “to be announced” (TBA) market (MBS TBAs), the seller agrees to deliver mortgage-backed securities for an agreed upon price on an agreed upon date, but may make no guarantee as to the specific securities to be delivered. In lieu of taking delivery of mortgage-backed securities, the Fund could enter into dollar rolls, which are transactions in which the Fund sells securities to a counterparty and simultaneously agrees to purchase those or similar securities in the future at a predetermined price. Dollar rolls involve the risk that the market value of the securities the Fund is obligated to repurchase may decline below the repurchase price, or that the counterparty may default on its obligations. These transactions may also increase the Fund’s portfolio turnover rate. If the Fund reinvests the proceeds of the security sold, the Fund will also be subject to the risk that the investments purchased with such proceeds will decline in value (a form of leverage risk). MBS TBAs and dollar rolls are subject to counterparty risk (the risk that the counterparty to the instrument will not perform or be able to perform in accordance with the terms of the instrument).

Mortgage- and Other Asset-Backed Securities Risk. The value of any mortgage-backed and other asset-backed securities held by the Fund may be affected by, among other things, changes or perceived changes in: interest rates; factors concerning the interests in and structure of the issuer or the originator of the mortgages or other assets; the creditworthiness of the entities that provide any supporting letters of credit, surety bonds or other credit enhancements; or the market's assessment of the quality of underlying assets. Payment of principal and interest on some mortgage-backed securities (but not the market value of the securities themselves) may be guaranteed by the full faith and credit of a particular U.S. Government agency, authority, enterprise or instrumentality, and some, but not all, are also insured or guaranteed by the U.S. Government. Mortgage-backed securities issued by non-governmental issuers (such as commercial banks, savings and loan institutions, private mortgage insurance companies, mortgage bankers and other secondary market issuers) may entail greater risk than obligations guaranteed by the U.S. Government. Mortgage- and other asset-backed securities are subject to prepayment risk, which is the possibility that the underlying mortgage or other asset may be refinanced or prepaid prior to maturity during periods of declining or low interest rates, causing the Fund to have to reinvest the money received in securities that have lower yields. Rising or high interest rates tend to extend the duration of mortgage- and other asset-backed securities, making their prices more volatile and more sensitive to changes in interest rates.

Stripped Securities Risk. Stripped securities are the separate income or principal components of debt securities. These securities are particularly sensitive to changes in interest rates, and therefore subject to greater fluctuations in price than typical interest bearing debt securities.

Prepayment and Extension Risk. Prepayment and extension risk is the risk that a bond or other security or investment might, in the case of prepayment risk, be called or otherwise converted, prepaid or redeemed before maturity and, in the case of extension risk, the investment might not be called as expected, and the portfolio managers may not be able to invest the proceeds in other investments providing as high a level of income, resulting in a reduced yield to the Fund. In the case of mortgage- or asset-backed securities, as interest rates decrease or spreads narrow, the likelihood of prepayment increases. Conversely, extension risk is the risk that an unexpected rise in interest rates will extend the life of a mortgage- or asset-backed security beyond the prepayment time. If the Fund’s investments are locked in at a lower interest rate for a longer period of time, the portfolio managers may be unable to capitalize on securities with higher interest rates or wider spreads.

Reinvestment Risk. Reinvestment risk is the risk that the Fund will not be able to reinvest income or principal at the same return it is currently earning.

Depositary Receipts Risk. Depositary receipts are receipts issued by a bank or trust company reflecting ownership of underlying securities issued by foreign companies. Some foreign securities are traded in the form of American Depositary Receipts (ADRs). Depositary receipts involve risks similar to the risks associated with investments in foreign securities, including those associated with the particular country, which may be related to the particular political, regulatory, economic, social and other conditions or events occurring in the country and fluctuations in its currency, as well as market risk tied to the underlying foreign company. In addition, ADR holders may have limited voting rights, may not have the same rights afforded typical company stockholders in the event of a corporate action such as an acquisition, merger or rights offering and may experience difficulty in receiving company stockholder communications.

Derivatives Risk/Futures Contracts Risk. The loss that may be incurred in entering into futures contracts may exceed the amount of the premium paid and may be potentially unlimited. Futures markets are highly volatile and the use of futures may increase the volatility of the Fund’s NAV. Additionally, as a result of the low collateral deposits normally involved in futures trading, a relatively small price movement in a futures contract may result in substantial losses for the Fund. Futures contracts may be illiquid. Furthermore, exchanges may limit fluctuations in futures contract prices during a trading session by imposing a maximum permissible price movement on each futures contract. The Fund may be disadvantaged if it is prohibited from executing a trade outside the daily permissible price movement. Futures contracts executed on foreign exchanges may not provide the same protection as U.S. exchanges. These transactions involve additional risks, including counterparty risk, hedging risk and pricing risk.

Changing Distribution Level Risk. The amount of the distributions paid by the Fund will vary and generally depends on the amount of interest income and/or dividends received by the Fund on the securities it holds. The Fund may not be able to pay distributions or may have to reduce its distribution level if the interest income and/or dividends the Fund receives from its investments decline.

Rule 144A Securities Risk. The Fund may invest significantly in privately placed “Rule 144A” securities that are determined to be liquid in accordance with procedures adopted by the Fund’s Board. However, an insufficient number of qualified institutional buyers interested in purchasing Rule 144A securities at a particular time could affect adversely the marketability of such securities and the Fund might be unable to dispose of such securities promptly or at reasonable prices. Accordingly, even if determined to be liquid, the Fund’s holdings of Rule 144A securities may increase the level of Fund illiquidity if eligible buyers become uninterested in buying them at a particular time. Issuers of Rule 144A securities are required to furnish information to potential investors upon request. However, the required disclosure is much less extensive than that required of public companies and is not publicly available since it is not filed with the SEC. Further, issuers of Rule 144A securities can require recipients of the information (such as the Fund) to agree contractually to keep the information confidential, which could also adversely affect the Fund’s ability to dispose of the security.

Frequent Trading Risk. The portfolio managers may actively and frequently trade investments in the Fund's portfolio to carry out its investment strategies. Frequent trading of investments increases the possibility that the Fund, as relevant, will realize taxable capital gains (including short-term capital gains, which are generally taxable to shareholders at higher rates than long-term capital gains for U.S. federal income tax purposes), which could reduce the Fund's after-tax return. Frequent trading can also mean higher brokerage and other transaction costs, which could reduce the Fund's return. The trading costs and tax effects associated with portfolio turnover may adversely affect the Fund’s performance.

Select Portfolio Risk. Because the Fund may invest in a limited number of companies, the Fund as a whole is subject to greater risk of loss if any of its portfolio securities decline in price. In addition, the Fund’s holdings and weightings will diverge significantly from its primary benchmark’s holdings and weightings and the Fund may therefore experience greater risk and volatility relative to the benchmark. Because the Fund may invest in more than one company concentrated in a similar industry, sector or geographic region, the Fund may be even more concentrated than the number of companies it may hold would suggest.

Index Risk. The Fund's value will generally decline when the performance of its targeted index declines. In addition, because the Fund may not hold all issues included in its index, it may not always be fully invested. The Fund also bears advisory, administrative and other expenses and transaction costs in trading securities, which the index does not bear. Accordingly, the Fund's performance will likely fail to match the performance of its targeted index, after taking expenses into account. It is not possible to invest directly in an index.

Highly Leveraged Transactions Risk. The loans or other securities in which the Fund invests may include highly leveraged transactions whereby the borrower assumes large amounts of debt in order to have the financial resources to attempt to achieve its business objectives. Loans or securities that are part of highly leveraged transactions involve a greater risk (including default and bankruptcy) than other investments.

Issuer Risk. An issuer in which the Fund invests or to which it has exposure may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors.

Risk Lose Money [Text]

rr_RiskLoseMoney

There is no assurance that the Fund will achieve its investment objective and you may lose money.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with those of the S&P 500^® Index, the Fund’s primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund’s primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500^® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund’s performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund’s performance compares to an equally weighted custom composite of the Fund’s primary equity and primary debt benchmarks, the S&P 500^® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund’s assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund’s portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities.

The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes.

The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with those of the S&P 500^® Index, the Fund’s primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund’s primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500^® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund’s performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund’s performance compares to an equally weighted custom composite of the Fund’s primary equity and primary debt benchmarks, the S&P 500^® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund’s assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund’s portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table below the bar chart compares the Fund’s returns for the periods shown with those of the S&P 500^® Index, the Fund’s primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund’s primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500^® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund’s performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund’s performance compares to an equally weighted custom composite of the Fund’s primary equity and primary debt benchmarks, the S&P 500^® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund’s assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund’s portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800.345.6611

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

columbiathreadneedle.com/us

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Year by Year Total Return (%)
as of December 31 Each Year

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best and Worst Quarterly Returns
During the Period Shown in the Bar Chart

Best                            2nd Quarter 2009                            19.33%

Worst                         4th Quarter 2008                            -19.26%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs).

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

The after-tax returns are shown only for Class Z shares and will vary for other share classes.

Columbia Thermostat Fund | Class A

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

Management fees

rr_ManagementFeesOverAssets

0.10%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.16%

Acquired fund fees and expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.52%

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.03%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.01%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.02%

Expenses Deferred Charges [Text Block]

rr_ExpensesDeferredChargesTextBlock

This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

1 year

rr_ExpenseExampleYear01

673

3 years

rr_ExpenseExampleYear03

883

5 years

rr_ExpenseExampleYear05

1,110

10 years

rr_ExpenseExampleYear10

1,761

1 year

rr_ExpenseExampleNoRedemptionYear01

673

3 years

rr_ExpenseExampleNoRedemptionYear03

883

5 years

rr_ExpenseExampleNoRedemptionYear05

1,110

10 years

rr_ExpenseExampleNoRedemptionYear10

1,761

1 Year

rr_AverageAnnualReturnYear01

(0.75%)

5 Years

rr_AverageAnnualReturnYear05

8.54%

10 Years

rr_AverageAnnualReturnYear10

5.66%

Share Class Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 03, 2003

Columbia Thermostat Fund | Class B

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

5.00%

^[4]

Management fees

rr_ManagementFeesOverAssets

0.10%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.75%

Other expenses

rr_OtherExpensesOverAssets

0.31%

Acquired fund fees and expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.52%

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.68%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.16%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.52%

Expenses Deferred Charges [Text Block]

rr_ExpensesDeferredChargesTextBlock

This charge decreases over time.

1 year

rr_ExpenseExampleYear01

655

3 years

rr_ExpenseExampleYear03

814

5 years

rr_ExpenseExampleYear05

1,098

10 years

rr_ExpenseExampleYear10

1,801

1 year

rr_ExpenseExampleNoRedemptionYear01

155

3 years

rr_ExpenseExampleNoRedemptionYear03

514

5 years

rr_ExpenseExampleNoRedemptionYear05

898

10 years

rr_ExpenseExampleNoRedemptionYear10

1,801

1 Year

rr_AverageAnnualReturnYear01

(0.17%)

5 Years

rr_AverageAnnualReturnYear05

9.00%

10 Years

rr_AverageAnnualReturnYear10

5.73%

Share Class Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 03, 2003

Columbia Thermostat Fund | Class C

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[5]

Management fees

rr_ManagementFeesOverAssets

0.10%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.16%

Acquired fund fees and expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.52%

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.78%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.01%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.77%

Expenses Deferred Charges [Text Block]

rr_ExpensesDeferredChargesTextBlock

This charge applies to redemptions within one year after purchase, with certain limited exceptions.

1 year

rr_ExpenseExampleYear01

280

3 years

rr_ExpenseExampleYear03

559

5 years

rr_ExpenseExampleYear05

964

10 years

rr_ExpenseExampleYear10

2,094

1 year

rr_ExpenseExampleNoRedemptionYear01

180

3 years

rr_ExpenseExampleNoRedemptionYear03

559

5 years

rr_ExpenseExampleNoRedemptionYear05

964

10 years

rr_ExpenseExampleNoRedemptionYear10

2,094

1 Year

rr_AverageAnnualReturnYear01

3.50%

5 Years

rr_AverageAnnualReturnYear05

9.00%

10 Years

rr_AverageAnnualReturnYear10

5.49%

Share Class Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 03, 2003

Columbia Thermostat Fund | Class R4

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.10%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.16%

Acquired fund fees and expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.52%

Total annual Fund operating expenses

rr_ExpensesOverAssets

0.78%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.01%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.77%

1 year

rr_ExpenseExampleYear01

79

3 years

rr_ExpenseExampleYear03

248

5 years

rr_ExpenseExampleYear05

432

10 years

rr_ExpenseExampleYear10

965

1 year

rr_ExpenseExampleNoRedemptionYear01

79

3 years

rr_ExpenseExampleNoRedemptionYear03

248

5 years

rr_ExpenseExampleNoRedemptionYear05

432

10 years

rr_ExpenseExampleNoRedemptionYear10

965

1 Year

rr_AverageAnnualReturnYear01

5.61%

5 Years

rr_AverageAnnualReturnYear05

10.09%

10 Years

rr_AverageAnnualReturnYear10

6.55%

Share Class Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 08, 2012

Columbia Thermostat Fund | Class R5

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.10%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.14%

Acquired fund fees and expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.52%

Total annual Fund operating expenses

rr_ExpensesOverAssets

0.76%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

none

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.76%

1 year

rr_ExpenseExampleYear01

78

3 years

rr_ExpenseExampleYear03

243

5 years

rr_ExpenseExampleYear05

422

10 years

rr_ExpenseExampleYear10

942

1 year

rr_ExpenseExampleNoRedemptionYear01

78

3 years

rr_ExpenseExampleNoRedemptionYear03

243

5 years

rr_ExpenseExampleNoRedemptionYear05

422

10 years

rr_ExpenseExampleNoRedemptionYear10

942

1 Year

rr_AverageAnnualReturnYear01

5.62%

5 Years

rr_AverageAnnualReturnYear05

10.11%

10 Years

rr_AverageAnnualReturnYear10

6.56%

Share Class Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 08, 2012

Columbia Thermostat Fund | Class Y

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.10%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.09%

Acquired fund fees and expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.52%

Total annual Fund operating expenses

rr_ExpensesOverAssets

0.71%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

none

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.71%

1 year

rr_ExpenseExampleYear01

73

3 years

rr_ExpenseExampleYear03

227

5 years

rr_ExpenseExampleYear05

395

10 years

rr_ExpenseExampleYear10

883

1 year

rr_ExpenseExampleNoRedemptionYear01

73

3 years

rr_ExpenseExampleNoRedemptionYear03

227

5 years

rr_ExpenseExampleNoRedemptionYear05

395

10 years

rr_ExpenseExampleNoRedemptionYear10

883

1 Year

rr_AverageAnnualReturnYear01

5.68%

5 Years

rr_AverageAnnualReturnYear05

10.14%

10 Years

rr_AverageAnnualReturnYear10

6.57%

Share Class Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 08, 2012

Columbia Thermostat Fund | Class Z

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.10%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.15%

Acquired fund fees and expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.52%

Total annual Fund operating expenses

rr_ExpensesOverAssets

0.77%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

none

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.77%

1 year

rr_ExpenseExampleYear01

79

3 years

rr_ExpenseExampleYear03

246

5 years

rr_ExpenseExampleYear05

428

10 years

rr_ExpenseExampleYear10

954

1 year

rr_ExpenseExampleNoRedemptionYear01

79

3 years

rr_ExpenseExampleNoRedemptionYear03

246

5 years

rr_ExpenseExampleNoRedemptionYear05

428

10 years

rr_ExpenseExampleNoRedemptionYear10

954

2005

rr_AnnualReturn2005

5.50%

^[6]

2006

rr_AnnualReturn2006

10.86%

^[6]

2007

rr_AnnualReturn2007

8.49%

^[6]

2008

rr_AnnualReturn2008

(30.53%)

^[6]

2009

rr_AnnualReturn2009

32.29%

^[6]

2010

rr_AnnualReturn2010

17.58%

^[6]

2011

rr_AnnualReturn2011

4.85%

^[6]

2012

rr_AnnualReturn2012

13.69%

^[6]

2013

rr_AnnualReturn2013

9.30%

^[6]

2014

rr_AnnualReturn2014

5.57%

^[6]

Year to Date Return, Label

rr_YearToDateReturnLabel

Year to Date return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2015

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

1.50%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

19.33%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(19.26%)

1 Year

rr_AverageAnnualReturnYear01

5.57%

5 Years

rr_AverageAnnualReturnYear05

10.09%

10 Years

rr_AverageAnnualReturnYear10

6.55%

Share Class Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

Columbia Thermostat Fund | returns after taxes on distributions | Class Z

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

4.15%

5 Years

rr_AverageAnnualReturnYear05

8.98%

10 Years

rr_AverageAnnualReturnYear10

5.13%

Share Class Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

Columbia Thermostat Fund | returns after taxes on distributions and sale of Fund shares | Class Z

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

3.34%

5 Years

rr_AverageAnnualReturnYear05

7.70%

10 Years

rr_AverageAnnualReturnYear10

4.83%

Share Class Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 25, 2002

Columbia Thermostat Fund | S&P 500® Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

13.69%

5 Years

rr_AverageAnnualReturnYear05

15.45%

10 Years

rr_AverageAnnualReturnYear10

7.67%

Columbia Thermostat Fund | Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

5.97%

5 Years

rr_AverageAnnualReturnYear05

4.45%

10 Years

rr_AverageAnnualReturnYear10

4.71%

Columbia Thermostat Fund | Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

4.31%

5 Years

rr_AverageAnnualReturnYear05

8.80%

10 Years

rr_AverageAnnualReturnYear10

6.11%

Columbia Thermostat Fund | 50/50 Blended Benchmark (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

9.85%

5 Years

rr_AverageAnnualReturnYear05

10.09%

10 Years

rr_AverageAnnualReturnYear10

6.48%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] "Total annual Fund operating expenses" include acquired fund (Portfolio Fund) fees and expenses (expenses the Fund incurs indirectly through its investments in other funds) and may be higher than "Total Net Expenses" shown in the Financial Highlights section of this prospectus because "Total Net Expenses" do not include Portfolio Fund (acquired fund) fees and expenses.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund's investment in the Portfolio Funds (acquired funds)), do not exceed the annual rates of 0.50% for Class A shares, 1.00% for Class B shares, 1.25% for Class C shares, 0.25% for Class R4 shares, 0.24% for Class R5 shares, 0.19% for Class Y shares and 0.25% for Class Z shares, through April 30, 2016. This arrangement may only be modified or amended with approval from all parties to the arrangement, including the Fund and the Investment Manager.

[4] This charge decreases over time.

[5] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[6] Year to Date return as of March 31, 2015: 1.50%

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2015
Columbia Acorn European Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY OF THE FUND
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Columbia Acorn European FundSM (the Fund) seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 22 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 30, 2016
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 74% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	74.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 22 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that: you invest $10,000 in the applicable class of Fund shares for the periods indicated, your investment has a 5% return each year, and the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above. Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first year of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in European companies. Under normal circumstances, the Fund invests at least 70% of its total assets in companies in Western European countries (for example, the United Kingdom, Germany, France and Italy), but also may invest up to 30% of its total assets in companies in emerging Central and Eastern European countries (for example, Poland, the Czech Republic, Turkey and Cyprus), including up to 10% of its total assets in companies in Russia and the Ukraine. For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, a European country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in a European country or countries or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector. Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $5 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $5 billion at the time of initial investment. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time. The Investment Manager typically seeks companies with: A strong business franchise that offers growth potential. Products and services in which the company has a competitive advantage. A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company. The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down. Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives. Liquidity and Trading Volume Risk. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance. Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies. Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility. Geographic Concentration Risk/Europe Risk. The Fund may be particularly susceptible to economic, political, regulatory or other events or conditions affecting issuers and countries in Europe. Currency devaluations could occur in countries that have not yet experienced currency devaluation to date, or could continue to occur in countries that have already experienced such devaluations. In addition, the private and public sectors’ debt problems of a single European Union (EU) country can pose significant economic risks to the EU as a whole. As a result, the Fund’s NAV may be more volatile than the NAV of a more geographically diversified fund. If securities of issuers in Europe fall out of favor, it may cause the Fund to underperform other funds that do not concentrate in this region of the world. Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar. Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers. Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking. Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations. Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations. Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar. Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility. Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors. Special Situations Risk. Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, may be exposed to heightened risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Certain “special situation” investments are investments in securities or other instruments that are determined to be illiquid or lacking a readily ascertainable fair value. Certain special situation investments prevent ownership interests therein from being withdrawn until the special situation investment, or a portion thereof, is realized or deemed realized, which may negatively impact Fund performance. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.
Risk Lose Money [Text]	rr_RiskLoseMoney	There is no assurance that the Fund will achieve its investment objective and you may lose money.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Standard & Poor’s (S&P) Europe Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, and the Euromoney Smaller European Companies (inc. UK) Index. The S&P Europe Between $500 Million and $5 Billion® Index is representative of the institutionally investable capital of 17 European countries (as of December 31, 2014), as determined by S&P, with market caps ranging between $500 million to $5 billion. The Euromoney Smaller European Companies (inc. UK) Index is an index of smaller companies in Europe including the UK market. The Euromoney Smaller European Companies Index covers companies of small- and mid-cap market capitalization in Europe's developed markets. The index is rebalanced on a quarterly basis. The performance of the Euromoney Smaller European Companies (inc UK) Index is provided to show how the Fund’s performance compares to a widely recognized index of small-capitalization equity performance in European markets. The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities. The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares. The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Standard & Poor’s (S&P) Europe Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, and the Euromoney Smaller European Companies (inc. UK) Index. The S&P Europe Between $500 Million and $5 Billion® Index is representative of the institutionally investable capital of 17 European countries (as of December 31, 2014), as determined by S&P, with market caps ranging between $500 million to $5 billion. The Euromoney Smaller European Companies (inc. UK) Index is an index of smaller companies in Europe including the UK market. The Euromoney Smaller European Companies Index covers companies of small- and mid-cap market capitalization in Europe's developed markets. The index is rebalanced on a quarterly basis. The performance of the Euromoney Smaller European Companies (inc UK) Index is provided to show how the Fund’s performance compares to a widely recognized index of small-capitalization equity performance in European markets.
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	The table below the bar chart compares the Fund’s returns for the periods shown with the Standard & Poor’s (S&P) Europe Between $500 Million and $5 Billion® Index, the Fund's primary benchmark, and the Euromoney Smaller European Companies (inc. UK) Index. The S&P Europe Between $500 Million and $5 Billion® Index is representative of the institutionally investable capital of 17 European countries (as of December 31, 2014), as determined by S&P, with market caps ranging between $500 million to $5 billion. The Euromoney Smaller European Companies (inc. UK) Index is an index of smaller companies in Europe including the UK market. The Euromoney Smaller European Companies Index covers companies of small- and mid-cap market capitalization in Europe's developed markets. The index is rebalanced on a quarterly basis. The performance of the Euromoney Smaller European Companies (inc UK) Index is provided to show how the Fund’s performance compares to a widely recognized index of small-capitalization equity performance in European markets.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800.345.6611
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	columbiathreadneedle.com/us
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Year by Year Total Return (%) as of December 31 Each Year
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best and Worst Quarterly Returns During the Period Shown in the Bar Chart Best                            1st Quarter 2012                            17.69% Worst                         3rd Quarter 2014                            -9.07%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs).
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	The after-tax returns are shown only for Class Z shares and will vary for other share classes.
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.
Columbia Acorn European Fund | Class A
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[1]
Management fees	rr_ManagementFeesOverAssets	1.19%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.61%
Total annual Fund operating expenses	rr_ExpensesOverAssets	2.05%
Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.30%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.75%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	743
3 years	rr_ExpenseExampleYear03	1,153
5 years	rr_ExpenseExampleYear05	1,589
10 years	rr_ExpenseExampleYear10	2,795
1 year	rr_ExpenseExampleNoRedemptionYear01	743
3 years	rr_ExpenseExampleNoRedemptionYear03	1,153
5 years	rr_ExpenseExampleNoRedemptionYear05	1,589
10 years	rr_ExpenseExampleNoRedemptionYear10	2,795
1 Year	rr_AverageAnnualReturnYear01	(13.09%)
Life of Fund	rr_AverageAnnualReturnSinceInception	10.15%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 19, 2011
Columbia Acorn European Fund | Class C
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[3]
Management fees	rr_ManagementFeesOverAssets	1.19%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.63%
Total annual Fund operating expenses	rr_ExpensesOverAssets	2.82%
Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.32%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	2.50%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge applies to redemptions within one year after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	353
3 years	rr_ExpenseExampleYear03	844
5 years	rr_ExpenseExampleYear05	1,461
10 years	rr_ExpenseExampleYear10	3,124
1 year	rr_ExpenseExampleNoRedemptionYear01	253
3 years	rr_ExpenseExampleNoRedemptionYear03	844
5 years	rr_ExpenseExampleNoRedemptionYear05	1,461
10 years	rr_ExpenseExampleNoRedemptionYear10	3,124
1 Year	rr_AverageAnnualReturnYear01	(9.35%)
Life of Fund	rr_AverageAnnualReturnSinceInception	11.28%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 19, 2011
Columbia Acorn European Fund | Class I
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	1.19%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.50%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.69%
Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.28%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.41%
1 year	rr_ExpenseExampleYear01	144
3 years	rr_ExpenseExampleYear03	505
5 years	rr_ExpenseExampleYear05	892
10 years	rr_ExpenseExampleYear10	1,974
1 year	rr_ExpenseExampleNoRedemptionYear01	144
3 years	rr_ExpenseExampleNoRedemptionYear03	505
5 years	rr_ExpenseExampleNoRedemptionYear05	892
10 years	rr_ExpenseExampleNoRedemptionYear10	1,974
1 Year	rr_AverageAnnualReturnYear01	(7.49%)
Life of Fund	rr_AverageAnnualReturnSinceInception	12.43%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 19, 2011
Columbia Acorn European Fund | Class R4
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	1.19%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.62%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.81%
Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.31%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.50%
1 year	rr_ExpenseExampleYear01	153
3 years	rr_ExpenseExampleYear03	539
5 years	rr_ExpenseExampleYear05	951
10 years	rr_ExpenseExampleYear10	2,101
1 year	rr_ExpenseExampleNoRedemptionYear01	153
3 years	rr_ExpenseExampleNoRedemptionYear03	539
5 years	rr_ExpenseExampleNoRedemptionYear05	951
10 years	rr_ExpenseExampleNoRedemptionYear10	2,101
1 Year	rr_AverageAnnualReturnYear01	(7.49%)
Life of Fund	rr_AverageAnnualReturnSinceInception	12.41%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Jun. 25, 2014
Columbia Acorn European Fund | Class R5
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	1.19%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.55%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.74%
Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.28%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.46%
1 year	rr_ExpenseExampleYear01	149
3 years	rr_ExpenseExampleYear03	521
5 years	rr_ExpenseExampleYear05	918
10 years	rr_ExpenseExampleYear10	2,029
1 year	rr_ExpenseExampleNoRedemptionYear01	149
3 years	rr_ExpenseExampleNoRedemptionYear03	521
5 years	rr_ExpenseExampleNoRedemptionYear05	918
10 years	rr_ExpenseExampleNoRedemptionYear10	2,029
1 Year	rr_AverageAnnualReturnYear01	(7.54%)
Life of Fund	rr_AverageAnnualReturnSinceInception	12.39%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn European Fund | Class Z
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	1.19%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.60%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.79%
Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.29%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.50%
1 year	rr_ExpenseExampleYear01	153
3 years	rr_ExpenseExampleYear03	535
5 years	rr_ExpenseExampleYear05	943
10 years	rr_ExpenseExampleYear10	2,081
1 year	rr_ExpenseExampleNoRedemptionYear01	153
3 years	rr_ExpenseExampleNoRedemptionYear03	535
5 years	rr_ExpenseExampleNoRedemptionYear05	943
10 years	rr_ExpenseExampleNoRedemptionYear10	2,081
2012	rr_AnnualReturn2012	25.66%	[4]
2013	rr_AnnualReturn2013	33.98%	[4]
2014	rr_AnnualReturn2014	(7.52%)	[4]
Year to Date Return, Label	rr_YearToDateReturnLabel	Year to Date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2015
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	4.39%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2012
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	17.69%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2014
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(9.07%)
1 Year	rr_AverageAnnualReturnYear01	(7.52%)
Life of Fund	rr_AverageAnnualReturnSinceInception	12.40%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 19, 2011
Columbia Acorn European Fund | returns after taxes on distributions | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(7.59%)
Life of Fund	rr_AverageAnnualReturnSinceInception	12.27%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 19, 2011
Columbia Acorn European Fund | returns after taxes on distributions and sale of Fund shares | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(3.86%)
Life of Fund	rr_AverageAnnualReturnSinceInception	9.86%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 19, 2011
Columbia Acorn European Fund | S&P Europe Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(5.35%)
Life of Fund	rr_AverageAnnualReturnSinceInception	13.80%
Columbia Acorn European Fund | Euromoney Smaller European Companies (inc UK) Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(7.67%)
Life of Fund	rr_AverageAnnualReturnSinceInception	11.72%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rates of 1.75% for Class A shares, 2.50% for Class C shares, 1.41% for Class I shares, 1.50% for Class R4 shares, 1.46% for Class R5 shares and 1.50% for Class Z shares, through April 30, 2016.This arrangement may only be modified or amended with approval from all parties to the arrangement, including the Fund and the Investment Manager.

[3] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[4] Year to Date return as of March 31, 2015: 4.39%

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	485BPOS
Document Period End Date	dei_DocumentPeriodEndDate	Dec. 31, 2014
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Central Index Key	dei_EntityCentralIndexKey	0000002110
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Apr. 30, 2015
Document Effective Date	dei_DocumentEffectiveDate	May 01, 2015
Prospectus Date	rr_ProspectusDate	May 01, 2015

XML

Columbia Acorn Fund

SUMMARY OF THE FUND

Investment Objective

Columbia Acorn^® Fund (the Fund) seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 21 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Columbia Acorn Fund	Class A		Class B		Class C		Class I	Class R4	Class R5	Class Y	Class Z
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%		none		none		none	none	none	none	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00%	[1]	5.00%	[2]	1.00%	[3]	none	none	none	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Columbia Acorn Fund	Class A	Class B	Class C	Class I	Class R4	Class R5	Class Y	Class Z
Management fees	0.64%	0.64%	0.64%	0.64%	0.64%	0.64%	0.64%	0.64%
Distribution and/or service (12b-1) fees	0.25%	0.75%	1.00%	none	none	none	none	none
Other expenses	0.19%	0.37%	0.14%	0.07%	0.20%	0.12%	0.07%	0.15%
Total annual Fund operating expenses	1.08%	1.76%	1.78%	0.71%	0.84%	0.76%	0.71%	0.79%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in the applicable class of Fund shares for the periods indicated,

• your investment has a 5% return each year, and

• the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

Expense Example Columbia Acorn Fund (USD $)	1 year	3 years	5 years	10 years
Class A	679	899	1,136	1,816
Class B	679	854	1,154	1,894
Class C	281	560	964	2,095
Class I	73	227	395	883
Class R4	86	268	466	1,037
Class R5	78	243	422	942
Class Y	73	227	395	883
Class Z	81	252	439	978

Expense Example, No Redemption Columbia Acorn Fund (USD $)	1 year	3 years	5 years	10 years
Class A	679	899	1,136	1,816
Class B	179	554	954	1,894
Class C	181	560	964	2,095
Class I	73	227	395	883
Class R4	86	268	466	1,037
Class R5	78	243	422	942
Class Y	73	227	395	883
Class Z	81	252	439	978

Portfolio Turnover

The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 17% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $5 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $5 billion at the time of initial investment.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services in which the company has a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down.

Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives.

Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies.

Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors.

Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility.

Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations.

Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades.

Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations.

Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights.

Liquidity and Trading Volume Risk. Because the Fund may invest a percentage of its assets in foreign securities, it may be subject to the liquidity and trading volume risks associated with international investing. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell foreign portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell these securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in foreign portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance.

Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with those of the Russell 2500 Index, the Fund’s primary benchmark, the Russell 2000 Index and the Standard & Poor’s (S&P) 500^® Index. The Russell 2500 Index measures the performance of the 2,500 smallest companies in the Russell 3000 Index, which represents approximately 17% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The Russell 2000 Index shows how the Fund’s performance compares to a widely recognized index of companies with somewhat lower capitalization than the Fund’s primary benchmark. The S&P 500^® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in small and mid-sized companies, the comparison to the S&P 500^® Index is presented to show performance against a widely recognized broad-based market index.

The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities.

The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.

Year by Year Total Return (%)
as of December 31 Each Year

Best and Worst Quarterly Returns
During the Period Shown in the Bar Chart

Best                            2nd Quarter 2009                            20.90%

Worst                         4th Quarter 2008                            -25.11%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)

Average Annual Total Returns Columbia Acorn Fund	Share Class Inception Date	1 Year	5 Years	10 Years
Class Z	Jun. 10, 1970	0.82%	13.35%	8.39%
Class Z returns after taxes on distributions	Jun. 10, 1970	(2.85%)	11.70%	7.21%
Class Z returns after taxes on distributions and sale of Fund shares	Jun. 10, 1970	3.43%	10.77%	6.90%
Class A	Oct. 16, 2000	(5.23%)	11.69%	7.44%
Class B	Oct. 16, 2000	(4.27%)	12.08%	7.41%
Class C	Oct. 16, 2000	(0.98%)	12.18%	7.25%
Class I	Sep. 27, 2010	0.91%	13.41%	8.42%
Class R4	Nov. 08, 2012	0.81%	13.33%	8.38%
Class R5	Nov. 08, 2012	0.89%	13.37%	8.40%
Class Y	Nov. 08, 2012	0.94%	13.39%	8.41%
Russell 2500 Index (reflects no deductions for fees, expenses or taxes)		7.07%	16.36%	8.72%
Russell 2000 Index (reflects no deductions for fees, expenses or taxes)		4.89%	15.55%	7.77%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)		13.69%	15.45%	7.67%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge decreases over time.

[3] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[1] Year to Date return as of March 31, 2015: 3.97%

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2015
Document Creation Date	dei_DocumentCreationDate	Apr. 30, 2015

XML

Columbia Acorn International Select

SUMMARY OF THE FUND

Investment Objective

Columbia Acorn International Select^SM (the Fund) seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 22 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Columbia Acorn International Select	Class A		Class B		Class C		Class I	Class R4	Class R5	Class Y	Class Z
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%		none		none		none	none	none	none	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00%	[1]	5.00%	[2]	1.00%	[3]	none	none	none	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Columbia Acorn International Select		Class A	Class B	Class C	Class I	Class R4	Class R5	Class Y	Class Z
Management fees		0.94%	0.94%	0.94%	0.94%	0.94%	0.94%	0.94%	0.94%
Distribution and/or service (12b-1) fees		0.25%	0.75%	1.00%	none	none	none	none	none
Other expenses		0.27%	0.42%	0.29%	0.15%	0.26%	0.20%	0.15%	0.23%
Acquired fund fees and expenses		0.01%	0.01%	0.01%	0.01%	0.01%	0.01%	0.01%	0.01%
Total annual Fund operating expenses	[1]	1.47%	2.12%	2.24%	1.10%	1.21%	1.15%	1.10%	1.18%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in the applicable class of Fund shares for the periods indicated,

• your investment has a 5% return each year, and

• the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

Expense Example Columbia Acorn International Select (USD $)	1 year	3 years	5 years	10 years
Class A	716	1,013	1,332	2,231
Class B	715	964	1,339	2,286
Class C	327	700	1,200	2,575
Class I	112	350	606	1,340
Class R4	123	384	665	1,466
Class R5	117	365	633	1,398
Class Y	112	350	606	1,340
Class Z	120	375	649	1,432

Expense Example, No Redemption Columbia Acorn International Select (USD $)	1 year	3 years	5 years	10 years
Class A	716	1,013	1,332	2,231
Class B	215	664	1,139	2,286
Class C	227	700	1,200	2,575
Class I	112	350	606	1,340
Class R4	123	384	665	1,466
Class R5	117	365	633	1,398
Class Y	112	350	606	1,340
Class Z	120	375	649	1,432

Portfolio Turnover

The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 58% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 65% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom).

The Fund also may invest up to 35% of its total assets in companies in emerging markets (for example, China, India and Brazil). The Fund generally invests in at least three countries other than the United States but may invest up to 25% of its total assets in securities of U.S. issuers.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $25 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $25 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $25 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $25 billion at the time of initial investment.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $25 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund also may invest in larger-sized companies.

The Fund invests in a limited number of foreign companies (generally between 40-60), offering the potential to provide above-average growth over time. In pursuit of the Fund’s objective, the portfolio managers will take advantage of the research and stock-picking capabilities of the Investment Manager and will generally concentrate the Fund’s investments in those sectors, companies, geographic regions or industries that the portfolio managers believe offer the best investment return potential.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services in which the company has a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down.

Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.

Select Portfolio Risk. Because the Fund may invest in a limited number of companies, the Fund as a whole is subject to greater risk of loss if any of its portfolio securities decline in price. In addition, the Fund’s holdings and weightings will diverge significantly from its primary benchmark’s holdings and weightings and the Fund may therefore experience greater risk and volatility relative to the benchmark. Because the Fund may invest in more than one company concentrated in a similar industry, sector or geographic region, the Fund may be even more concentrated than the number of companies it may hold would suggest.

Liquidity and Trading Volume Risk. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance.

Real Estate-Related Investment Risk. Investments in real estate investment trusts (REITs) and in securities of other companies (wherever organized) principally engaged in the real estate industry subject the Fund to, among other things, risks similar to those of direct investments in real estate and the real estate industry in general. These include risks related to general and local economic conditions, possible lack of availability of financing and changes in interest rates or property values. REITs are entities that either own properties or make construction or mortgage loans, and also may include operating or finance companies. The value of interests in a REIT may be affected by, among other factors, changes in the value of the underlying properties owned by the REIT, changes in the prospect for earnings and/or cash flow growth of the REIT itself, defaults by borrowers or tenants, market saturation, decreases in market rates for rents, and other economic, political, or regulatory matters affecting the real estate industry, including REITs. REITs and similar non-U.S. entities depend upon specialized management skills, may have limited financial resources, may have less trading volume in their securities, and may be subject to more abrupt or erratic price movements than the overall securities markets. REITs are also subject to the risk of failing to qualify for favorable tax treatment under the Internal Revenue Code of 1986, as amended. Some REITs (especially mortgage REITs) are affected by risks similar to those associated with investments in debt securities including changes in interest rates and the quality of credit extended.

Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations.

Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades.

Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations.

Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights.

Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies.

Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors.

Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility.

Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with those of the Standard & Poor’s (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion^® Index, the Fund’s primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion^® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund’s performance compares to a widely recognized broad based index of foreign market performance.

The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities.

The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.

Year by Year Total Return (%)
as of December 31 Each Year

Best and Worst Quarterly Returns
During the Period Shown in the Bar Chart

Best                            2nd Quarter 2009                            23.44%

Worst                         3rd Quarter 2008                            -24.76%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)

Average Annual Total Returns Columbia Acorn International Select	Share Class Inception Date	1 Year	5 Years	10 Years
Class Z	Nov. 23, 1998	(6.79%)	7.57%	7.76%
Class Z returns after taxes on distributions	Nov. 23, 1998	(9.33%)	5.78%	6.71%
Class Z returns after taxes on distributions and sale of Fund shares	Nov. 23, 1998	(1.47%)	6.16%	6.52%
Class A	Oct. 16, 2000	(12.39%)	5.95%	6.78%
Class B	Oct. 16, 2000	(11.77%)	6.23%	6.73%
Class C	Oct. 16, 2000	(8.61%)	6.37%	6.57%
Class I	Sep. 27, 2010	(6.72%)	7.63%	7.79%
Class R4	Nov. 08, 2012	(6.83%)	7.55%	7.75%
Class R5	Nov. 08, 2012	(6.77%)	7.58%	7.77%
Class Y	Nov. 08, 2012	(6.71%)	7.60%	7.78%
S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)		(2.10%)	7.53%	6.25%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)		(4.90%)	5.33%	4.43%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge decreases over time.

[3] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[1] "Total annual Fund operating expenses" include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than "Total Net Expenses" shown in the Financial Highlights section of this prospectus because "Total Net Expenses" do not include acquired fund fees and expenses.

[1] Year to Date return as of March 31, 2015: 1.48%

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Columbia Acorn International

SUMMARY OF THE FUND

Investment Objective

Columbia Acorn International^® (the Fund) seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 21 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Columbia Acorn International	Class A		Class B		Class C		Class I	Class R	Class R4	Class R5	Class Y	Class Z
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%		none		none		none	none	none	none	none	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00%	[1]	5.00%	[2]	1.00%	[3]	none	none	none	none	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Columbia Acorn International	Class A	Class B	Class C	Class I	Class R	Class R4	Class R5	Class Y	Class Z
Management fees	0.75%	0.75%	0.75%	0.75%	0.75%	0.75%	0.75%	0.75%	0.75%
Distribution and/or service (12b-1) fees	0.25%	0.75%	1.00%	none	0.50%	none	none	none	none
Other expenses	0.26%	0.50%	0.23%	0.10%	0.37%	0.28%	0.15%	0.10%	0.18%
Total annual Fund operating expenses	1.26%	2.00%	1.98%	0.85%	1.62%	1.03%	0.90%	0.85%	0.93%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in the applicable class of Fund shares for the periods indicated,

• your investment has a 5% return each year, and

• the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

Expense Example Columbia Acorn International (USD $)	1 year	3 years	5 years	10 years
Class A	696	952	1,227	2,010
Class B	703	927	1,278	2,136
Class C	301	621	1,068	2,306
Class I	87	271	471	1,049
Class R	165	511	881	1,922
Class R4	105	328	569	1,259
Class R5	92	287	498	1,108
Class Y	87	271	471	1,049
Class Z	95	296	515	1,143

Expense Example, No Redemption Columbia Acorn International (USD $)	1 year	3 years	5 years	10 years
Class A	696	952	1,227	2,010
Class B	203	627	1,078	2,136
Class C	201	621	1,068	2,306
Class I	87	271	471	1,049
Class R	165	511	881	1,922
Class R4	105	328	569	1,259
Class R5	92	287	498	1,108
Class Y	87	271	471	1,049
Class Z	95	296	515	1,143

Portfolio Turnover

The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 28% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 75% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil).

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $5 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $5 billion at the time of initial investment.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services in which the company has a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down.

Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives.

Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies.

Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility.

Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations.

Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades.

Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations.

Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights.

Liquidity and Trading Volume Risk. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.

Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with those of the Standard & Poor’s (S&P) Global Ex-U.S. Between $500 Million and $5 Billion^® Index, the Fund’s primary benchmark, the S&P Global Ex-U.S. SmallCap^® Index and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Global Ex-U.S. Between $500 Million and $5 Billion^® Index is a subset of the broad market selected by the index sponsor that represents the mid- and small-cap developed and emerging markets, excluding the United States. The S&P Global Ex-U.S. SmallCap^® Index is an unmanaged index consisting of the bottom 20% of institutionally investable capital of developed and emerging countries, excluding the United States. The performance of the S&P Global Ex-U.S. Small Cap^® Index is provided to show how the Fund’s performance compares to foreign market performance with a similar geographic distribution and wider market cap range than the Fund’s primary benchmark. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund’s performance compares to a widely recognized broad based index of foreign market performance.

The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities.

The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.

Year by Year Total Return (%)
as of December 31 Each Year

Best and Worst Quarterly Returns
During the Period Shown in the Bar Chart

Best                            2nd Quarter 2009                            33.30%

Worst                         3rd Quarter 2008                            -23.68%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)

Average Annual Total Returns Columbia Acorn International	Share Class Inception Date	1 Year	5 Years	10 Years
Class Z	Sep. 23, 1992	(4.28%)	8.47%	8.95%
Class Z returns after taxes on distributions	Sep. 23, 1992	(5.65%)	7.55%	8.06%
Class Z returns after taxes on distributions and sale of Fund shares	Sep. 23, 1992	(0.99%)	6.76%	7.49%
Class A	Oct. 16, 2000	(10.05%)	6.84%	7.95%
Class B	Oct. 16, 2000	(9.75%)	7.06%	7.87%
Class C	Oct. 16, 2000	(6.16%)	7.31%	7.76%
Class I	Sep. 27, 2010	(4.20%)	8.54%	8.99%
Class R	Aug. 02, 2011	(4.95%)	7.76%	8.26%
Class R4	Nov. 08, 2012	(4.39%)	8.43%	8.94%
Class R5	Aug. 02, 2011	(4.25%)	8.48%	8.95%
Class Y	Nov. 08, 2012	(4.21%)	8.50%	8.97%
S&P Global ex-U.S. Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)		(1.76%)	7.14%	7.65%
S&P Global Ex-U.S. SmallCap® Index (reflects no deductions for fees, expenses or taxes)		(3.11%)	7.41%	7.27%
MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)		(4.90%)	5.33%	4.43%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge decreases over time.

[3] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[1] Year to Date return as of March 31, 2015: 4.34%

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2015
Columbia Acorn Select
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY OF THE FUND
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Columbia Acorn SelectSM (the Fund) seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 22 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 30, 2016
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 17% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	17.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 22 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that: you invest $10,000 in the applicable class of Fund shares for the periods indicated, your investment has a 5% return each year, and the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above. Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first year of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal circumstances, the Fund invests a majority of its net assets in the common stock of companies with market capitalizations under $20 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $20 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $20 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $20 billion at the time of initial investment. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $20 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Colombia). The Fund invests in a limited number of companies (generally between 30-60), offering the potential to provide above-average growth over time. In pursuit of the Fund’s objective, the portfolio managers may take advantage of the research and stock-picking capabilities of the Investment Manager to select investments that are “best ideas,” but need not do so and will generally concentrate the Fund’s investments in those sectors, companies, geographic regions or industries that the portfolio managers believe offer the most growth potential. The Investment Manager typically seeks companies with: A strong business franchise that offers growth potential. Products and services in which the company has a competitive advantage. A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company. The Fund may also invest in companies that the Investment Manager believes have good operational fundamentals but that the Investment Manager believes are undervalued due to negative investor sentiment related to company-specific or market-related conditions. Investments in turnaround and development stage companies may also be made when the Investment Manager believes potential returns outweigh risks of losses. The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down. Select Portfolio Risk. Because the Fund may invest in a limited number of companies, the Fund as a whole is subject to greater risk of loss if any of its portfolio securities decline in price. In addition, the Fund’s holdings and weightings will diverge significantly from its primary benchmark’s holdings and weightings and the Fund may therefore experience greater risk and volatility relative to the benchmark. Because the Fund may invest in more than one company concentrated in a similar industry, sector or geographic region, the Fund may be even more concentrated than the number of companies it may hold would suggest. Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives. Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility. Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies. Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors. Opportunistic Investing Risk. Undervalued securities involve the risk that they may never reach their expected full market value, either because the market fails to recognize the security's intrinsic worth or the expected value was misgauged. Undervalued securities also may decline in price even though the Investment Manager believes they are already undervalued. Turnaround companies may never improve their fundamentals, may take much longer than expected to improve, or may improve much less than expected. Development stage companies could fail to develop and deplete their assets, resulting in large percentage losses. Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility. Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar. Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers. Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking. Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations. Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations. Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Liquidity and Trading Volume Risk. Because the Fund may invest a percentage of its assets in foreign securities, it may be subject to the liquidity and trading volume risks associated with international investing. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell foreign portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell these securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in foreign portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance. Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.
Risk Lose Money [Text]	rr_RiskLoseMoney	There is no assurance that the Fund will achieve its investment objective and you may lose money.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Standard & Poor’s (S&P) MidCap 400® Index, the Fund’s primary benchmark, and the S&P 500® Index. The S&P MidCap 400® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index. The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities. The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares. The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Standard & Poor’s (S&P) MidCap 400® Index, the Fund’s primary benchmark, and the S&P 500® Index. The S&P MidCap 400® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index.
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	The table below the bar chart compares the Fund’s returns for the periods shown with the Standard & Poor’s (S&P) MidCap 400® Index, the Fund’s primary benchmark, and the S&P 500® Index. The S&P MidCap 400® Index is a market value-weighted index that tracks the performance of 400 mid-cap U.S. companies. The S&P 500® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. Although the Fund typically invests in companies with market capitalizations under $20 billion at the time of investment, the comparison to the S&P 500® Index is presented to show performance against a widely recognized market index.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800.345.6611
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	columbiathreadneedle.com/us
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Year by Year Total Return (%) as of December 31 Each Year
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best and Worst Quarterly Returns During the Period Shown in the Bar Chart Best                            2nd Quarter 2009                            28.11% Worst                         4th Quarter 2008                            -30.14%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs).
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	The after-tax returns are shown only for Class Z shares and will vary for other share classes.
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.
Columbia Acorn Select | Class A
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[1]
Management fees	rr_ManagementFeesOverAssets	0.85%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.22%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.32%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.20%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.12%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	683
3 years	rr_ExpenseExampleYear03	951
5 years	rr_ExpenseExampleYear05	1,239
10 years	rr_ExpenseExampleYear10	2,057
1 year	rr_ExpenseExampleNoRedemptionYear01	683
3 years	rr_ExpenseExampleNoRedemptionYear03	951
5 years	rr_ExpenseExampleNoRedemptionYear05	1,239
10 years	rr_ExpenseExampleNoRedemptionYear10	2,057
1 Year	rr_AverageAnnualReturnYear01	(3.70%)
5 Years	rr_AverageAnnualReturnYear05	8.98%
10 Years	rr_AverageAnnualReturnYear10	6.39%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn Select | Class B
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	5.00%	[3]
Management fees	rr_ManagementFeesOverAssets	0.85%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.75%
Other expenses	rr_OtherExpensesOverAssets	0.55%
Total annual Fund operating expenses	rr_ExpensesOverAssets	2.15%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.20%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.95%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge decreases over time.
1 year	rr_ExpenseExampleYear01	698
3 years	rr_ExpenseExampleYear03	954
5 years	rr_ExpenseExampleYear05	1,336
10 years	rr_ExpenseExampleYear10	2,256
1 year	rr_ExpenseExampleNoRedemptionYear01	198
3 years	rr_ExpenseExampleNoRedemptionYear03	654
5 years	rr_ExpenseExampleNoRedemptionYear05	1,136
10 years	rr_ExpenseExampleNoRedemptionYear10	2,256
1 Year	rr_AverageAnnualReturnYear01	(2.60%)
5 Years	rr_AverageAnnualReturnYear05	9.30%
10 Years	rr_AverageAnnualReturnYear10	6.31%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn Select | Class C
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[4]
Management fees	rr_ManagementFeesOverAssets	0.85%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.19%
Total annual Fund operating expenses	rr_ExpensesOverAssets	2.04%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.20%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.84%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge applies to redemptions within one year after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	287
3 years	rr_ExpenseExampleYear03	620
5 years	rr_ExpenseExampleYear05	1,080
10 years	rr_ExpenseExampleYear10	2,353
1 year	rr_ExpenseExampleNoRedemptionYear01	187
3 years	rr_ExpenseExampleNoRedemptionYear03	620
5 years	rr_ExpenseExampleNoRedemptionYear05	1,080
10 years	rr_ExpenseExampleNoRedemptionYear10	2,353
1 Year	rr_AverageAnnualReturnYear01	0.63%
5 Years	rr_AverageAnnualReturnYear05	9.45%
10 Years	rr_AverageAnnualReturnYear10	6.19%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn Select | Class I
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.85%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.10%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.95%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.20%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	0.75%
1 year	rr_ExpenseExampleYear01	77
3 years	rr_ExpenseExampleYear03	283
5 years	rr_ExpenseExampleYear05	506
10 years	rr_ExpenseExampleYear10	1,148
1 year	rr_ExpenseExampleNoRedemptionYear01	77
3 years	rr_ExpenseExampleNoRedemptionYear03	283
5 years	rr_ExpenseExampleNoRedemptionYear05	506
10 years	rr_ExpenseExampleNoRedemptionYear10	1,148
1 Year	rr_AverageAnnualReturnYear01	2.49%
5 Years	rr_AverageAnnualReturnYear05	10.69%
10 Years	rr_AverageAnnualReturnYear10	7.38%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 27, 2010
Columbia Acorn Select | Class R4
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.85%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.27%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.12%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.20%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	0.92%
1 year	rr_ExpenseExampleYear01	94
3 years	rr_ExpenseExampleYear03	336
5 years	rr_ExpenseExampleYear05	598
10 years	rr_ExpenseExampleYear10	1,345
1 year	rr_ExpenseExampleNoRedemptionYear01	94
3 years	rr_ExpenseExampleNoRedemptionYear03	336
5 years	rr_ExpenseExampleNoRedemptionYear05	598
10 years	rr_ExpenseExampleNoRedemptionYear10	1,345
1 Year	rr_AverageAnnualReturnYear01	2.39%
5 Years	rr_AverageAnnualReturnYear05	10.58%
10 Years	rr_AverageAnnualReturnYear10	7.32%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn Select | Class R5
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.85%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.15%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.00%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.20%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	0.80%
1 year	rr_ExpenseExampleYear01	82
3 years	rr_ExpenseExampleYear03	298
5 years	rr_ExpenseExampleYear05	533
10 years	rr_ExpenseExampleYear10	1,206
1 year	rr_ExpenseExampleNoRedemptionYear01	82
3 years	rr_ExpenseExampleNoRedemptionYear03	298
5 years	rr_ExpenseExampleNoRedemptionYear05	533
10 years	rr_ExpenseExampleNoRedemptionYear10	1,206
1 Year	rr_AverageAnnualReturnYear01	2.50%
5 Years	rr_AverageAnnualReturnYear05	10.62%
10 Years	rr_AverageAnnualReturnYear10	7.34%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn Select | Class Y
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.85%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.10%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.95%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.20%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	0.75%
1 year	rr_ExpenseExampleYear01	77
3 years	rr_ExpenseExampleYear03	283
5 years	rr_ExpenseExampleYear05	506
10 years	rr_ExpenseExampleYear10	1,148
1 year	rr_ExpenseExampleNoRedemptionYear01	77
3 years	rr_ExpenseExampleNoRedemptionYear03	283
5 years	rr_ExpenseExampleNoRedemptionYear05	506
10 years	rr_ExpenseExampleNoRedemptionYear10	1,148
1 Year	rr_AverageAnnualReturnYear01	2.53%
5 Years	rr_AverageAnnualReturnYear05	10.64%
10 Years	rr_AverageAnnualReturnYear10	7.35%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn Select | Class Z
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.85%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.19%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.04%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.20%)	[2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	0.84%
1 year	rr_ExpenseExampleYear01	86
3 years	rr_ExpenseExampleYear03	311
5 years	rr_ExpenseExampleYear05	555
10 years	rr_ExpenseExampleYear10	1,253
1 year	rr_ExpenseExampleNoRedemptionYear01	86
3 years	rr_ExpenseExampleNoRedemptionYear03	311
5 years	rr_ExpenseExampleNoRedemptionYear05	555
10 years	rr_ExpenseExampleNoRedemptionYear10	1,253
2005	rr_AnnualReturn2005	11.08%	[5]
2006	rr_AnnualReturn2006	19.68%	[5]
2007	rr_AnnualReturn2007	9.20%	[5]
2008	rr_AnnualReturn2008	(49.18%)	[5]
2009	rr_AnnualReturn2009	66.17%	[5]
2010	rr_AnnualReturn2010	22.88%	[5]
2011	rr_AnnualReturn2011	(16.37%)	[5]
2012	rr_AnnualReturn2012	17.15%	[5]
2013	rr_AnnualReturn2013	34.16%	[5]
2014	rr_AnnualReturn2014	2.47%	[5]
Year to Date Return, Label	rr_YearToDateReturnLabel	Year to Date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2015
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	2.83%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	28.11%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(30.14%)
1 Year	rr_AverageAnnualReturnYear01	2.47%
5 Years	rr_AverageAnnualReturnYear05	10.60%
10 Years	rr_AverageAnnualReturnYear10	7.33%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 23, 1998
Columbia Acorn Select | returns after taxes on distributions | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(2.20%)
5 Years	rr_AverageAnnualReturnYear05	7.98%
10 Years	rr_AverageAnnualReturnYear10	5.89%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 23, 1998
Columbia Acorn Select | returns after taxes on distributions and sale of Fund shares | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	5.17%
5 Years	rr_AverageAnnualReturnYear05	8.33%
10 Years	rr_AverageAnnualReturnYear10	5.93%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 23, 1998
Columbia Acorn Select | S&P MidCap 400® Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	9.77%
5 Years	rr_AverageAnnualReturnYear05	16.54%
10 Years	rr_AverageAnnualReturnYear10	9.71%
Columbia Acorn Select | S&P 500® Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	13.69%
5 Years	rr_AverageAnnualReturnYear05	15.45%
10 Years	rr_AverageAnnualReturnYear10	7.67%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] Effective May 1, 2015, Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive 0.20% of the advisory fee otherwise payable to it by the Fund through April 30, 2016. This arrangement may only be modified or amended with approval from all parties to the arrangement, including the Fund and the Investment Manager.

[3] This charge decreases over time.

[4] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[5] Year to Date return as of March 31, 2015: 2.83%

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2015
Columbia Acorn International Select
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY OF THE FUND
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Columbia Acorn International SelectSM (the Fund) seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 22 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 58% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	58.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 22 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	50,000
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]	rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees	“Total annual Fund operating expenses” include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than “Total Net Expenses” shown in the Financial Highlights section of this prospectus because “Total Net Expenses” do not include acquired fund fees and expenses.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that: you invest $10,000 in the applicable class of Fund shares for the periods indicated, your investment has a 5% return each year, and the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal circumstances, the Fund invests at least 65% of its net assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom). The Fund also may invest up to 35% of its total assets in companies in emerging markets (for example, China, India and Brazil). The Fund generally invests in at least three countries other than the United States but may invest up to 25% of its total assets in securities of U.S. issuers. Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $25 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $25 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $25 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $25 billion at the time of initial investment. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $25 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund also may invest in larger-sized companies. The Fund invests in a limited number of foreign companies (generally between 40-60), offering the potential to provide above-average growth over time. In pursuit of the Fund’s objective, the portfolio managers will take advantage of the research and stock-picking capabilities of the Investment Manager and will generally concentrate the Fund’s investments in those sectors, companies, geographic regions or industries that the portfolio managers believe offer the best investment return potential. The Investment Manager typically seeks companies with: A strong business franchise that offers growth potential. Products and services in which the company has a competitive advantage. A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company. The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down. Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives. Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility. Select Portfolio Risk. Because the Fund may invest in a limited number of companies, the Fund as a whole is subject to greater risk of loss if any of its portfolio securities decline in price. In addition, the Fund’s holdings and weightings will diverge significantly from its primary benchmark’s holdings and weightings and the Fund may therefore experience greater risk and volatility relative to the benchmark. Because the Fund may invest in more than one company concentrated in a similar industry, sector or geographic region, the Fund may be even more concentrated than the number of companies it may hold would suggest. Liquidity and Trading Volume Risk. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance. Real Estate-Related Investment Risk. Investments in real estate investment trusts (REITs) and in securities of other companies (wherever organized) principally engaged in the real estate industry subject the Fund to, among other things, risks similar to those of direct investments in real estate and the real estate industry in general. These include risks related to general and local economic conditions, possible lack of availability of financing and changes in interest rates or property values. REITs are entities that either own properties or make construction or mortgage loans, and also may include operating or finance companies. The value of interests in a REIT may be affected by, among other factors, changes in the value of the underlying properties owned by the REIT, changes in the prospect for earnings and/or cash flow growth of the REIT itself, defaults by borrowers or tenants, market saturation, decreases in market rates for rents, and other economic, political, or regulatory matters affecting the real estate industry, including REITs. REITs and similar non-U.S. entities depend upon specialized management skills, may have limited financial resources, may have less trading volume in their securities, and may be subject to more abrupt or erratic price movements than the overall securities markets. REITs are also subject to the risk of failing to qualify for favorable tax treatment under the Internal Revenue Code of 1986, as amended. Some REITs (especially mortgage REITs) are affected by risks similar to those associated with investments in debt securities including changes in interest rates and the quality of credit extended. Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar. Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers. Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking. Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations. Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades. Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations. Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights. Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies. Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors. Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility. Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.
Risk Lose Money [Text]	rr_RiskLoseMoney	There is no assurance that the Fund will achieve its investment objective and you may lose money.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with those of the Standard & Poor’s (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion® Index, the Fund’s primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund’s performance compares to a widely recognized broad based index of foreign market performance. The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities. The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares. The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with those of the Standard & Poor’s (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion® Index, the Fund’s primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund’s performance compares to a widely recognized broad based index of foreign market performance.
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	The table below the bar chart compares the Fund’s returns for the periods shown with those of the Standard & Poor’s (S&P) Developed Ex-U.S. Between $2 Billion and $10 Billion® Index, the Fund’s primary benchmark, and the MSCI Europe, Australasia and Far East (EAFE) Index (Net). The S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index is a subset of the broad market selected by the index sponsor that represents the mid-cap developed market excluding the United States. The MSCI EAFE Index (Net) is a capitalization-weighted index that tracks the total return of common stocks in 22 developed-market countries within Europe, Australasia and the Far East. The performance of the MSCI EAFE Index (Net) is provided to show how the Fund’s performance compares to a widely recognized broad based index of foreign market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800.345.6611
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	columbiathreadneedle.com/us
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Year by Year Total Return (%) as of December 31 Each Year
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best and Worst Quarterly Returns During the Period Shown in the Bar Chart Best                            2nd Quarter 2009                            23.44% Worst                         3rd Quarter 2008                            -24.76%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs).
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	The after-tax returns are shown only for Class Z shares and will vary for other share classes.
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.
Columbia Acorn International Select | Class A
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[1]
Management fees	rr_ManagementFeesOverAssets	0.94%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.27%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.47%	[2]
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	716
3 years	rr_ExpenseExampleYear03	1,013
5 years	rr_ExpenseExampleYear05	1,332
10 years	rr_ExpenseExampleYear10	2,231
1 year	rr_ExpenseExampleNoRedemptionYear01	716
3 years	rr_ExpenseExampleNoRedemptionYear03	1,013
5 years	rr_ExpenseExampleNoRedemptionYear05	1,332
10 years	rr_ExpenseExampleNoRedemptionYear10	2,231
1 Year	rr_AverageAnnualReturnYear01	(12.39%)
5 Years	rr_AverageAnnualReturnYear05	5.95%
10 Years	rr_AverageAnnualReturnYear10	6.78%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn International Select | Class B
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	5.00%	[3]
Management fees	rr_ManagementFeesOverAssets	0.94%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.75%
Other expenses	rr_OtherExpensesOverAssets	0.42%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total annual Fund operating expenses	rr_ExpensesOverAssets	2.12%	[2]
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge decreases over time.
1 year	rr_ExpenseExampleYear01	715
3 years	rr_ExpenseExampleYear03	964
5 years	rr_ExpenseExampleYear05	1,339
10 years	rr_ExpenseExampleYear10	2,286
1 year	rr_ExpenseExampleNoRedemptionYear01	215
3 years	rr_ExpenseExampleNoRedemptionYear03	664
5 years	rr_ExpenseExampleNoRedemptionYear05	1,139
10 years	rr_ExpenseExampleNoRedemptionYear10	2,286
1 Year	rr_AverageAnnualReturnYear01	(11.77%)
5 Years	rr_AverageAnnualReturnYear05	6.23%
10 Years	rr_AverageAnnualReturnYear10	6.73%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn International Select | Class C
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[4]
Management fees	rr_ManagementFeesOverAssets	0.94%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.29%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total annual Fund operating expenses	rr_ExpensesOverAssets	2.24%	[2]
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge applies to redemptions within one year after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	327
3 years	rr_ExpenseExampleYear03	700
5 years	rr_ExpenseExampleYear05	1,200
10 years	rr_ExpenseExampleYear10	2,575
1 year	rr_ExpenseExampleNoRedemptionYear01	227
3 years	rr_ExpenseExampleNoRedemptionYear03	700
5 years	rr_ExpenseExampleNoRedemptionYear05	1,200
10 years	rr_ExpenseExampleNoRedemptionYear10	2,575
1 Year	rr_AverageAnnualReturnYear01	(8.61%)
5 Years	rr_AverageAnnualReturnYear05	6.37%
10 Years	rr_AverageAnnualReturnYear10	6.57%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn International Select | Class I
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.94%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.15%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.10%	[2]
1 year	rr_ExpenseExampleYear01	112
3 years	rr_ExpenseExampleYear03	350
5 years	rr_ExpenseExampleYear05	606
10 years	rr_ExpenseExampleYear10	1,340
1 year	rr_ExpenseExampleNoRedemptionYear01	112
3 years	rr_ExpenseExampleNoRedemptionYear03	350
5 years	rr_ExpenseExampleNoRedemptionYear05	606
10 years	rr_ExpenseExampleNoRedemptionYear10	1,340
1 Year	rr_AverageAnnualReturnYear01	(6.72%)
5 Years	rr_AverageAnnualReturnYear05	7.63%
10 Years	rr_AverageAnnualReturnYear10	7.79%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 27, 2010
Columbia Acorn International Select | Class R4
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.94%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.26%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.21%	[2]
1 year	rr_ExpenseExampleYear01	123
3 years	rr_ExpenseExampleYear03	384
5 years	rr_ExpenseExampleYear05	665
10 years	rr_ExpenseExampleYear10	1,466
1 year	rr_ExpenseExampleNoRedemptionYear01	123
3 years	rr_ExpenseExampleNoRedemptionYear03	384
5 years	rr_ExpenseExampleNoRedemptionYear05	665
10 years	rr_ExpenseExampleNoRedemptionYear10	1,466
1 Year	rr_AverageAnnualReturnYear01	(6.83%)
5 Years	rr_AverageAnnualReturnYear05	7.55%
10 Years	rr_AverageAnnualReturnYear10	7.75%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn International Select | Class R5
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.94%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.20%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.15%	[2]
1 year	rr_ExpenseExampleYear01	117
3 years	rr_ExpenseExampleYear03	365
5 years	rr_ExpenseExampleYear05	633
10 years	rr_ExpenseExampleYear10	1,398
1 year	rr_ExpenseExampleNoRedemptionYear01	117
3 years	rr_ExpenseExampleNoRedemptionYear03	365
5 years	rr_ExpenseExampleNoRedemptionYear05	633
10 years	rr_ExpenseExampleNoRedemptionYear10	1,398
1 Year	rr_AverageAnnualReturnYear01	(6.77%)
5 Years	rr_AverageAnnualReturnYear05	7.58%
10 Years	rr_AverageAnnualReturnYear10	7.77%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn International Select | Class Y
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.94%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.15%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.10%	[2]
1 year	rr_ExpenseExampleYear01	112
3 years	rr_ExpenseExampleYear03	350
5 years	rr_ExpenseExampleYear05	606
10 years	rr_ExpenseExampleYear10	1,340
1 year	rr_ExpenseExampleNoRedemptionYear01	112
3 years	rr_ExpenseExampleNoRedemptionYear03	350
5 years	rr_ExpenseExampleNoRedemptionYear05	606
10 years	rr_ExpenseExampleNoRedemptionYear10	1,340
1 Year	rr_AverageAnnualReturnYear01	(6.71%)
5 Years	rr_AverageAnnualReturnYear05	7.60%
10 Years	rr_AverageAnnualReturnYear10	7.78%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn International Select | Class Z
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.94%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.23%
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.18%	[2]
1 year	rr_ExpenseExampleYear01	120
3 years	rr_ExpenseExampleYear03	375
5 years	rr_ExpenseExampleYear05	649
10 years	rr_ExpenseExampleYear10	1,432
1 year	rr_ExpenseExampleNoRedemptionYear01	120
3 years	rr_ExpenseExampleNoRedemptionYear03	375
5 years	rr_ExpenseExampleNoRedemptionYear05	649
10 years	rr_ExpenseExampleNoRedemptionYear10	1,432
2005	rr_AnnualReturn2005	15.98%	[5]
2006	rr_AnnualReturn2006	36.27%	[5]
2007	rr_AnnualReturn2007	21.86%	[5]
2008	rr_AnnualReturn2008	(42.10%)	[5]
2009	rr_AnnualReturn2009	31.52%	[5]
2010	rr_AnnualReturn2010	21.89%	[5]
2011	rr_AnnualReturn2011	(9.76%)	[5]
2012	rr_AnnualReturn2012	22.42%	[5]
2013	rr_AnnualReturn2013	14.75%	[5]
2014	rr_AnnualReturn2014	(6.79%)	[5]
Year to Date Return, Label	rr_YearToDateReturnLabel	Year to Date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2015
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	1.48%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	23.44%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(24.76%)
1 Year	rr_AverageAnnualReturnYear01	(6.79%)
5 Years	rr_AverageAnnualReturnYear05	7.57%
10 Years	rr_AverageAnnualReturnYear10	7.76%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 23, 1998
Columbia Acorn International Select | returns after taxes on distributions | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(9.33%)
5 Years	rr_AverageAnnualReturnYear05	5.78%
10 Years	rr_AverageAnnualReturnYear10	6.71%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 23, 1998
Columbia Acorn International Select | returns after taxes on distributions and sale of Fund shares | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(1.47%)
5 Years	rr_AverageAnnualReturnYear05	6.16%
10 Years	rr_AverageAnnualReturnYear10	6.52%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 23, 1998
Columbia Acorn International Select | S&P Developed Ex-U.S. Between $2 Billion and $10 Billion® Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(2.10%)
5 Years	rr_AverageAnnualReturnYear05	7.53%
10 Years	rr_AverageAnnualReturnYear10	6.25%
Columbia Acorn International Select | MSCI EAFE Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(4.90%)
5 Years	rr_AverageAnnualReturnYear05	5.33%
10 Years	rr_AverageAnnualReturnYear10	4.43%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] "Total annual Fund operating expenses" include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than "Total Net Expenses" shown in the Financial Highlights section of this prospectus because "Total Net Expenses" do not include acquired fund fees and expenses.

[3] This charge decreases over time.

[4] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[5] Year to Date return as of March 31, 2015: 1.48%

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Columbia Acorn European Fund

SUMMARY OF THE FUND

Investment Objective

Columbia Acorn European Fund^SM (the Fund) seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 22 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Columbia Acorn European Fund	Class A		Class C		Class I	Class R4	Class R5	Class Z
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%		none		none	none	none	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00%	[1]	1.00%	[2]	none	none	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Columbia Acorn European Fund		Class A	Class C	Class I	Class R4	Class R5	Class Z
Management fees		1.19%	1.19%	1.19%	1.19%	1.19%	1.19%
Distribution and/or service (12b-1) fees		0.25%	1.00%	none	none	none	none
Other expenses		0.61%	0.63%	0.50%	0.62%	0.55%	0.60%
Total annual Fund operating expenses		2.05%	2.82%	1.69%	1.81%	1.74%	1.79%
Fee waivers and/or expense reimbursements	[1]	(0.30%)	(0.32%)	(0.28%)	(0.31%)	(0.28%)	(0.29%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements		1.75%	2.50%	1.41%	1.50%	1.46%	1.50%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in the applicable class of Fund shares for the periods indicated,

• your investment has a 5% return each year, and

• the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first year of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

Expense Example Columbia Acorn European Fund (USD $)	1 year	3 years	5 years	10 years
Class A	743	1,153	1,589	2,795
Class C	353	844	1,461	3,124
Class I	144	505	892	1,974
Class R4	153	539	951	2,101
Class R5	149	521	918	2,029
Class Z	153	535	943	2,081

Expense Example, No Redemption Columbia Acorn European Fund (USD $)	1 year	3 years	5 years	10 years
Class A	743	1,153	1,589	2,795
Class C	253	844	1,461	3,124
Class I	144	505	892	1,974
Class R4	153	539	951	2,101
Class R5	149	521	918	2,029
Class Z	153	535	943	2,081

Portfolio Turnover

The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 74% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus any borrowing for investment purposes) in European companies. Under normal circumstances, the Fund invests at least 70% of its total assets in companies in Western European countries (for example, the United Kingdom, Germany, France and Italy), but also may invest up to 30% of its total assets in companies in emerging Central and Eastern European countries (for example, Poland, the Czech Republic, Turkey and Cyprus), including up to 10% of its total assets in companies in Russia and the Ukraine. For purposes of the Fund's policies, the Fund may invest in a company if (i) it is domiciled in, or the principal trading market for its securities is in, a European country, (ii) it derives 50% or more of its economic value from goods produced, sales made or services performed or has at least 50% of its assets in a European country or countries or (iii) it is a holding company that predominantly holds shares in such companies. The Fund may invest in a variety of countries, industries and sectors and does not attempt to invest a specific percentage of its assets in any given country, industry or sector.

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations under $5 billion at the time of initial investment. However, if the Fund's investments in such companies represent less than a majority of its net assets, the Fund may continue to hold and to make additional investments in an existing company in its portfolio even if that company's capitalization has grown to exceed $5 billion. Under normal circumstances, the Fund may invest in companies with market capitalizations above $5 billion at the time of initial investment, provided that immediately after that investment a majority of its net assets would be invested in companies whose market capitalizations were under $5 billion at the time of initial investment.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of companies with market capitalizations under $5 billion, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies.

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to initially invest in a limited number of companies (generally under 100), offering the potential to provide above-average growth over time.

The Investment Manager typically seeks companies with:

• A strong business franchise that offers growth potential.

• Products and services in which the company has a competitive advantage.

• A stock price the Investment Manager believes is reasonable relative to the assets and earning power of the company.

The Investment Manager may sell a portfolio holding if the security reaches the Investment Manager's price target, if the company has a deterioration of fundamentals, such as failing to meet key operating benchmarks, or if the Investment Manager believes other securities are more attractive. The Investment Manager also may sell a portfolio holding to fund redemptions.

Principal Risks

An investment in the Fund involves risk, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down.

Active Management Risk. The Investment Manager’s active management of the Fund could cause the Fund to underperform its benchmark index and/or other funds with similar investment objectives.

Liquidity and Trading Volume Risk. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance.

Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.

Geographic Concentration Risk/Europe Risk. The Fund may be particularly susceptible to economic, political, regulatory or other events or conditions affecting issuers and countries in Europe. Currency devaluations could occur in countries that have not yet experienced currency devaluation to date, or could continue to occur in countries that have already experienced such devaluations. In addition, the private and public sectors’ debt problems of a single European Union (EU) country can pose significant economic risks to the EU as a whole. As a result, the Fund’s NAV may be more volatile than the NAV of a more geographically diversified fund. If securities of issuers in Europe fall out of favor, it may cause the Fund to underperform other funds that do not concentrate in this region of the world.

Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations.

Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades.

Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations.

Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights.

Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility.

Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors.

Special Situations Risk. Securities of companies that are involved in an initial public offering or a major corporate event, such as a business consolidation or restructuring, may be exposed to heightened risk because of the high degree of uncertainty that can be associated with such events. Securities issued in initial public offerings often are issued by companies that are in the early stages of development, have a history of little or no revenues and may operate at a loss following the offering. It is possible that there will be no active trading market for the securities after the offering, and that the market price of the securities may be subject to significant and unpredictable fluctuations. Certain “special situation” investments are investments in securities or other instruments that are determined to be illiquid or lacking a readily ascertainable fair value. Certain special situation investments prevent ownership interests therein from being withdrawn until the special situation investment, or a portion thereof, is realized or deemed realized, which may negatively impact Fund performance. Investing in special situations may have a magnified effect on the performance of funds with small amounts of assets.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Standard & Poor’s (S&P) Europe Between $500 Million and $5 Billion^® Index, the Fund's primary benchmark, and the Euromoney Smaller European Companies (inc. UK) Index. The S&P Europe Between $500 Million and $5 Billion^® Index is representative of the institutionally investable capital of 17 European countries (as of December 31, 2014), as determined by S&P, with market caps ranging between $500 million to $5 billion. The Euromoney Smaller European Companies (inc. UK) Index is an index of smaller companies in Europe including the UK market. The Euromoney Smaller European Companies Index covers companies of small- and mid-cap market capitalization in Europe's developed markets. The index is rebalanced on a quarterly basis. The performance of the Euromoney Smaller European Companies (inc UK) Index is provided to show how the Fund’s performance compares to a widely recognized index of small-capitalization equity performance in European markets.

The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities.

The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.

The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.

Year by Year Total Return (%)
as of December 31 Each Year

Best and Worst Quarterly Returns
During the Period Shown in the Bar Chart

Best                            1st Quarter 2012                            17.69%

Worst                         3rd Quarter 2014                            -9.07%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)

Average Annual Total Returns Columbia Acorn European Fund	Share Class Inception Date	1 Year	Life of Fund
Class Z	Aug. 19, 2011	(7.52%)	12.40%
Class Z returns after taxes on distributions	Aug. 19, 2011	(7.59%)	12.27%
Class Z returns after taxes on distributions and sale of Fund shares	Aug. 19, 2011	(3.86%)	9.86%
Class A	Aug. 19, 2011	(13.09%)	10.15%
Class C	Aug. 19, 2011	(9.35%)	11.28%
Class I	Aug. 19, 2011	(7.49%)	12.43%
Class R4	Jun. 25, 2014	(7.49%)	12.41%
Class R5	Nov. 08, 2012	(7.54%)	12.39%
S&P Europe Between $500 Million and $5 Billion® Index (reflects no deductions for fees, expenses or taxes)		(5.35%)	13.80%
Euromoney Smaller European Companies (inc UK) Index (reflects no deductions for fees, expenses or taxes)		(7.67%)	11.72%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[1] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund's investment in other investment companies, if any) do not exceed the annual rates of 1.75% for Class A shares, 2.50% for Class C shares, 1.41% for Class I shares, 1.50% for Class R4 shares, 1.46% for Class R5 shares and 1.50% for Class Z shares, through April 30, 2016.This arrangement may only be modified or amended with approval from all parties to the arrangement, including the Fund and the Investment Manager.

[1] Year to Date return as of March 31, 2015: 4.39%

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Columbia Thermostat Fund

SUMMARY OF THE FUND

Investment Objective

Columbia Thermostat Fund^SM (the Fund) seeks long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 40 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Columbia Thermostat Fund	Class A		Class B		Class C		Class R4	Class R5	Class Y	Class Z
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%		none		none		none	none	none	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00%	[1]	5.00%	[2]	1.00%	[3]	none	none	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Columbia Thermostat Fund		Class A	Class B	Class C	Class R4	Class R5	Class Y	Class Z
Management fees		0.10%	0.10%	0.10%	0.10%	0.10%	0.10%	0.10%
Distribution and/or service (12b-1) fees		0.25%	0.75%	1.00%	none	none	none	none
Other expenses		0.16%	0.31%	0.16%	0.16%	0.14%	0.09%	0.15%
Acquired fund fees and expenses		0.52%	0.52%	0.52%	0.52%	0.52%	0.52%	0.52%
Total annual Fund operating expenses	[1]	1.03%	1.68%	1.78%	0.78%	0.76%	0.71%	0.77%
Fee waivers and/or expense reimbursements	[2]	(0.01%)	(0.16%)	(0.01%)	(0.01%)	none	none	none
Total annual Fund operating expenses after fee waivers and/or expense reimbursements		1.02%	1.52%	1.77%	0.77%	0.76%	0.71%	0.77%

Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in the applicable class of Fund shares for the periods indicated,

• your investment has a 5% return each year, and

• the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first year of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

Expense Example Columbia Thermostat Fund (USD $)	1 year	3 years	5 years	10 years
Class A	673	883	1,110	1,761
Class B	655	814	1,098	1,801
Class C	280	559	964	2,094
Class R4	79	248	432	965
Class R5	78	243	422	942
Class Y	73	227	395	883
Class Z	79	246	428	954

Expense Example, No Redemption Columbia Thermostat Fund (USD $)	1 year	3 years	5 years	10 years
Class A	673	883	1,110	1,761
Class B	155	514	898	1,801
Class C	180	559	964	2,094
Class R4	79	248	432	965
Class R5	78	243	422	942
Class Y	73	227	395	883
Class Z	79	246	428	954

Portfolio Turnover

The Fund will indirectly bear the expenses associated with portfolio turnover of the underlying Portfolio Funds in which the Fund invests. Each Portfolio Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A Portfolio Fund’s higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when its shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 95% of the average value of its portfolio.

Principal Investment Strategies

The Fund is primarily managed as a fund that invests in other funds (i.e., a “fund-of-funds”) that seeks to achieve its investment objective by investing its assets among a selected group of underlying stock and bond mutual funds for which Columbia Wanger Asset Management, LLC, the Fund’s investment adviser (the Investment Manager) or its affiliates, including Columbia Management Investment Advisers, LLC, serves as investment adviser or principal underwriter (the Portfolio Funds). Under normal circumstances, the Fund allocates at least 95% of its net assets (stock/bond assets) among the Portfolio Funds according to the current level of Standard & Poor’s (S&P) 500^® Index. Generally, when the S&P 500^® Index goes up in relation to predetermined ranges set by the Investment Manager, the Fund sells a portion of its stock funds and invests more in the bond funds and when the S&P 500^® Index goes down in relation to the ranges, the Fund increases its investment in the stock funds. Under normal circumstances, the Fund may invest up to 5% of net assets plus any cash received that day in cash, high quality short-term paper and government securities.

Many asset allocation funds typically move assets from stocks to bonds when the market goes up, and from bonds to stocks when the market goes down. Most asset allocation funds are run by sophisticated investment professionals, who make subjective decisions based on economic and financial data and complex graphs of market behavior. By contrast, the day-to-day investment decisions for the Fund are made according to a single predetermined rule. The temperature in your house is run by a single rule: your thermostat turns on the furnace if your house is too cold or turns on the air conditioner if your house is too warm. This Fund works the same way, so it is named Columbia Thermostat Fund.

Because the Fund invests according to a pre-set program, there is no need for subjective day-to-day management. Although another successful asset allocation strategy might do better than the Fund, the Fund is designed for those who doubt the wisdom of trying to “time” the market and are unsure of the long-term trend of the stock market. The Fund takes psychology out of investing; it avoids the temptation to buy more stocks because the stock market is currently going up or to sell stocks because the market is declining. The Fund operates continuously and substantially automatically, subject to periodic review of the pre-set program by the Investment Manager and the Fund’s Board of Trustees. As described more fully below, the Investment Manager has the authority to review the structure and allocation ranges of the stock/bond allocation table and to make any changes considered appropriate.

The Investment Manager chooses the Portfolio Funds to provide participation in the major sectors of the stock market and the portions of the bond market it believes will preserve capital and generate returns. If you believe that the stock market will tend to go up most of the time, then you should probably own a fully invested stock fund and use a buy-and-hold strategy. Buy-and-hold was an excellent strategy in the 1982-1999 bull market. However, there have been long periods in the past when buy-and-hold was not the best strategy, such as 1930-1954 and 1969-1981, when the market fluctuated but did not make significant new highs. The Fund may be a good investment choice for you if you believe that the market will fluctuate significantly and provide modest to no secular growth for many years.

The Fund invests its stock/bond assets among the Portfolio Funds according to an asset allocation table. The Investment Manager calibrates the allocation table such that stock percentages vary inversely with price-to-earnings ratios on “normalized” (long-term) earnings. Within a range of 10% to 90%, stock percentages rise towards maximum allocations as such price-to-earnings ratios fall towards historical lows, and stock percentages fall as such price-to-earnings ratios rise towards historical highs.

The Fund’s current allocation table is set forth below.

Stock/Bond Allocation Table
	How the Fund will Invest the Stock/Bond Assets
Level of the S&P 500® Index	Stock Percentage	Bond Percentage
over 2225	10%	90%
over 2150 – 2225	15%	85%
over 2075 – 2150	20%	80%
over 2000 – 2075	25%	75%
over 1925 – 2000	30%	70%
over 1850 – 1925	35%	65%
over 1775 – 1850	40%	60%
over 1700 – 1775	45%	55%
over 1625 – 1700	50%	50%
over 1550 – 1625	55%	45%
over 1475 – 1550	60%	40%
over 1400 – 1475	65%	35%
over 1325 – 1400	70%	30%
over 1250 – 1325	75%	25%
over 1175 – 1250	80%	20%
over 1100 – 1175	85%	15%
1100 and under	90%	10%

When the S&P 500^® Index moves into a new band on the table, the Fund will rebalance the stock/bond mix to reflect the new S&P 500^® Index price level by redeeming shares of some Portfolio Funds and purchasing shares of other Portfolio Funds. Any such rebalancing typically will be implemented promptly. However, there are two circumstances when a rebalancing may be implemented over a longer timeline. First, when a rebalancing or allocation table change would trigger a 10% point or greater change in stock and bond allocations or individual Portfolio Funds, the rebalancing may be implemented over a period of up to two weeks, if deemed by the Investment Manager to be in the best interest of shareholders. The second exception is a “31-day Rule;” in order to reduce taxable events, after the Fund has increased its percentage allocation to either stock funds or bond funds, it will not decrease that allocation for at least 31 days. Following a change in the Fund's stock/bond mix, if the S&P 500^® Index remains within the same band for a while, normal market fluctuations will change the values of the Fund's holdings of stock Portfolio Funds and bond Portfolio Funds. The Investment Manager will invest cash flows from sales (or redemptions) of Fund shares to bring the stock/bond mix back toward the allocation percentages for that S&P 500^® Index band. For example, if the S&P 500^® Index is in the 1150-1200 band, and the value of the holdings of the stock Portfolio Funds has dropped to 68% of the value of the holdings of all Portfolio Funds, the Investment Manager would invest new cash in the stock Portfolio Funds (or cash for redemptions would come from the bond Portfolio Funds). If the 31-day Rule is in effect, the Investment Manager will invest new cash at the stock/bond percentage allocation as of the latest rebalancing.

As an illustrative example, suppose the following:

Date	Level of the S&P 500® Index	How the Fund will invest the Stock/ Bond Assets
Nov. 1	We begin when the market is 1680	50% stocks, 50% bonds
Dec. 1	The S&P 500® goes to 1701	rebalance 45% stocks, 55% bonds
Dec. 6	The S&P 500® drops back to 1690	no reversal for 31 days
Jan. 2	The S&P 500® is at 1650	rebalance 50% stocks, 50% bonds
Jan. 20	The S&P 500® drops to 1620	rebalance 55% stocks, 45% bonds
	The market has made a continuation move by going through a second action level, not a reversal move, so the 31-day Rule does not apply in this case.
Jan. 30	The S&P 500® goes up to 1630	no reversal for 31 days
Feb. 20	The S&P 500® is at 1640	rebalance 50% stocks, 50% bonds

The following table shows the seven stock Portfolio Funds and four bond Portfolio Funds that the Fund currently uses in its “fund-of-funds” structure and the current allocation percentage for each Portfolio Fund within the stock or bond category. As described more fully below, the Investment Manager may substitute or add additional Portfolio Funds at any time, including funds introduced after the date of this prospectus. The allocation percentage within each stock/bond category is achieved by rebalancing the investments within the category whenever the S&P 500^® Index moves into a new band on the allocation table, subject to the 31-day Rule described above. The Fund does not liquidate its investment in one Portfolio Fund in order to invest in another Portfolio Fund except in connection with a rebalancing due to a move of the S&P 500^® Index into a new band (or due to a change by the Investment Manager in the stock/bond allocation table to the Portfolio Funds or to the relative allocation among them). Until a subsequent rebalancing, the Fund's investments in, and redemptions from, the stock Portfolio Funds or the bond Portfolio Funds are allocated among the Portfolio Funds in a manner that will reduce any deviation of the relative values of the Fund's holdings of the Funds from the allocation percentages shown below.

Allocation of Stock/Bond Asset Within Asset Classes
	Type of Fund	Allocation
Stock Funds
Columbia Acorn® Fund	Small/Mid-cap growth	10%
Columbia Acorn International®	Small/Mid-cap international growth	20%
Columbia Acorn SelectSM	Mid-cap growth	10%
Columbia Contrarian Core Fund	Large-cap blend	20%
Columbia Dividend Income Fund	Large-cap value	20%
Columbia Large Cap Enhanced Core Fund	Large-cap blend	10%
Columbia Select Large Cap Growth Fund	Large-cap growth	10%
Total		100%
Bond Funds	Type of Fund	Allocation
Columbia Income Opportunities Fund	High-yield bond	20%
Columbia Intermediate Bond Fund	Intermediate-term bond	20%
Columbia Short Term Bond Fund	Short term bond	40%
Columbia U.S. Government Mortgage Fund	Government bond	20%
Total		100%

See the Portfolio Funds Summary section of this prospectus for information about the Portfolio Funds’ investment objectives and principal investment strategies.

The Investment Manager has the authority to review the Portfolio Funds and the relative stock/bond allocation percentages among them and to make any changes considered appropriate.

Each of the Portfolio Funds is currently managed by the Investment Manager or its affiliates. The Fund does not pay any sales load on its purchases of shares of the Portfolio Funds. On an annual basis, or on an “emergency” basis if necessary, the Investment Manager reviews the structure, allocation percentages and Portfolio Funds and makes any changes considered appropriate. The Investment Manager typically addresses the following questions:

• Should the stock/bond allocation table be revised (perhaps because the stock market has made a long-term move outside of the bands set forth above)?

• Should there be a change in the Portfolio Funds or should there be a change in the percentage allocations among the stock/bond funds (perhaps because of a change of portfolio managers, change of investment style, change in relative valuation or a reorganization of a Portfolio Fund)?

Any such changes by the Investment Manager are expected to be infrequent.

Principal Risks

An investment in the Fund involves risk, including general risks relating to the investment in the Fund based on its investment process and its "fund-of-funds" structure, as well as specific risks related to the individual Portfolio Funds, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down.

Allocation Risk. The Investment Manager uses an asset allocation strategy in pursuing the Fund’s investment objective. There is a risk that the Fund's allocation among asset classes or investments will cause the Fund's shares to lose value or cause the Fund to underperform other funds with similar investment objectives and/or strategies, or that the investments themselves will not produce the returns expected.

Fund-of-Funds Risk. Determinations regarding asset classes or underlying funds and the Fund’s allocations thereto may not successfully achieve the Fund’s investment objective, in whole or in part. The ability of the Fund to realize its investment objective will depend, in large part, on the extent to which the underlying funds realize their investment objective. There is no guarantee that the underlying funds will achieve their respective investment objectives. The Fund is exposed to the same risks as the underlying funds in direct proportion to the allocation of its assets among the underlying funds. By investing in a combination of underlying funds, the Fund has exposure to the risks of many areas of the market. The performance of underlying funds could be adversely affected if other entities that invest in the same underlying funds make relatively large investments or redemptions in such underlying funds. The Fund, and its shareholders, indirectly bear a portion of the expenses of any funds in which the Fund invests. Because the expenses and costs of each underlying fund are shared by its investors, redemptions by other investors in an underlying fund could result in decreased economies of scale and increased operating expenses for such fund. The Investment Manager may have potential conflicts of interest in selecting affiliated funds over unaffiliated funds for investment by the Fund, and may also face potential conflicts of interest in selecting affiliated funds, because the fees the Investment Manager receives from some underlying funds may be higher than the fees paid by other underlying funds. Further, because of the Investment Manager’s confidence in its own strategies, investment philosophy and capacities, it will, in selecting underlying funds, at times prefer a fund in the Columbia Acorn Family of Funds over alternative investments. There can be no assurance, however, that a fund in the Columbia Acorn Family of Funds selected for inclusion in Columbia Thermostat Fund’s portfolio will, in fact, outperform similar funds managed by the Investment Manager’s affiliates.

The Fund is subject indirectly to the following risks of the Portfolio Funds:

Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Although equity securities generally tend to have greater price volatility than debt securities, under certain market conditions, debt securities may have comparable or greater price volatility.

Interest Rate Risk. Interest rate risk is the risk of losses attributable to changes in interest rates. In general, if prevailing interest rates rise, the values of debt securities tend to fall, and if interest rates fall, the values of debt securities tend to rise. Changes in the value of a debt security usually will not affect the amount of income the Fund receives from it but will usually affect the value of the Fund's shares. In general, the longer the maturity or duration of a debt security, the greater its sensitivity to changes in interest rates. Interest rate declines also may increase prepayments of debt obligations, which, in turn, would increase prepayment risk. Similarly, a period of rising interest rates may negatively impact the Fund’s performance. Actions by governments and central banking authorities can result in increases in interest rates. Such actions may negatively affect the value of fixed-income securities held by the Fund, resulting in a negative impact on the Fund's performance and NAV. Securities with floating interest rates are typically less sensitive to interest rate changes, but may decline in value if their interest rates do not rise as much as interest rates in general. Because rates on certain floating rate loans and other debt securities reset only periodically, changes in prevailing interest rates (and particularly sudden and significant changes) can be expected to cause fluctuations in the Fund’s NAV.

Credit Risk. The value of fixed-income securities, or other instruments or assets, may decline if the issuer thereof defaults or otherwise becomes unable or unwilling, or is perceived to be unable or unwilling, to honor its financial obligations, such as making payments to the Fund when due. Rating agencies assign credit ratings to certain fixed-income securities to indicate their credit risk. Lower quality or unrated securities held by the Fund may present increased credit risk as compared to higher-rated securities. Non-investment grade fixed-income securities (commonly called “high-yield” or “junk”) are subject to greater price fluctuations and are more likely to experience a default than investment grade securities and therefore may expose the Fund to increased credit risk. If the Fund purchases unrated securities, or if the ratings of securities held by the Fund are lowered after purchase, the Fund will depend on analysis of credit risk more heavily than usual.

High-Yield Securities Risk. Securities rated below investment grade (commonly called “high-yield” or “junk” bonds) and unrated securities of comparable quality expose the Fund to a greater risk of loss of principal and income than a fund that invests solely or primarily in investment grade securities. In addition, these investments have greater price fluctuations, are less liquid and are more likely to experience a default than higher-rated securities. High-yield securities are considered to be predominantly speculative with respect to the issuer’s capacity to pay interest and repay principal.

Value Securities Risk. Value securities are securities of companies that may have experienced, for example, adverse business, industry or other developments or may be subject to special risks that have caused the securities to be out of favor and, in turn, potentially undervalued. The market value of a portfolio security may not meet the Investment Manager’s perceived value assessment of that security, or may decline in price, even though the Investment Manager believes the securities are already undervalued. There is also a risk that it may take longer than expected for the value of these investments to rise to the portfolio manager’s perceived value. In addition, value securities, at times, may not perform as well as growth securities or the stock market in general, and may be out of favor with investors for varying periods of time.

Growth Securities Risk. Growth securities typically trade at a higher multiple of earnings than other types of equity securities. Accordingly, the market values of growth securities may never reach their expected market value and may decline in price. In addition, growth securities, at times, may not perform as well as value securities or the stock market in general, and may be out of favor with investors for varying periods of time.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.

Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. The performance of the Fund may be negatively impacted by fluctuations in a foreign currency’s strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of foreign sub-custodians. Some countries have limited governmental oversight and regulation, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. As a result, there is a risk that the security will not be delivered to the Fund or that payment will not be received. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

Share Blocking. In certain non-U.S. markets, an issuer’s securities are blocked from trading for a specified number of days before and, in certain instances, after a shareholder meeting. The blocking period can last up to several weeks. Share blocking may prevent the Fund from buying or selling securities during this period. As a consequence of these restrictions, the Investment Manager, on behalf of the Fund, may abstain from voting proxies in markets that require share blocking.

Emerging Market Securities Risk. Securities issued by foreign governments or companies in emerging market countries, such as China, Russia and certain countries in Eastern Europe, the Middle East, Asia, Latin America or Africa, are more likely to have greater exposure to the risks of investing in foreign securities that are described in Foreign Securities Risk. In addition, emerging market countries are more likely to experience instability resulting, for example, from rapid changes or developments in social, political, economic or other conditions. Their economies are usually less mature and their securities markets are typically less developed with more limited trading activity (i.e., lower trading volumes and less liquidity) than more developed countries. Emerging market securities tend to be more volatile than securities in more developed markets. Many emerging market countries are heavily dependent on international trade and have fewer trading partners, which makes them more sensitive to world commodity prices and economic downturns in other countries, and some have a higher risk of currency devaluations.

Operational and Settlement Risks of Securities in Emerging Markets. Foreign sub-custodians in emerging markets may be recently organized, lack extensive operating experience or lack effective government oversight or regulation. In addition, there may be legal restrictions or limitations on the ability of the Fund to recover assets held in custody by a foreign sub-custodian in the event of the bankruptcy of the sub-custodian. There may also be a greater risk that settlement may be delayed and that cash or securities of the Fund may be lost because of failures of or defects in the system, including fraud or corruption. Settlement systems in emerging markets also have a higher risk of failed trades.

Risks Related to Currencies and Corporate Actions in Emerging Markets. Risks related to currencies and corporate actions are also greater in emerging market countries than in developed countries. Emerging market currencies may not be traded and are subject to a higher risk of currency devaluations.

Risks Related to Corporate and Securities Laws in Emerging Markets. Securities laws in emerging markets may be relatively new and unsettled and, consequently, there is a risk of rapid and unpredictable change in laws regarding foreign investment, securities regulation, title to securities and shareholder rights.

Liquidity and Trading Volume Risk. Due to market conditions, including uncertainty regarding the price of a security, it may be difficult for the Fund to buy or sell portfolio securities at a desirable time or price, which could result in investment losses. This risk of portfolio illiquidity is heightened with respect to small- and mid-cap securities, generally, and foreign small- and mid-cap securities in particular. The Fund may have to lower the selling price, liquidate other investments, or forego another, more appealing investment opportunity as a result of illiquidity in the markets. As a result of significant and sustained reductions in emerging and developed international market trading volumes in the wake of the 2007-2009 financial crisis, it may take longer to buy or sell securities, which can exacerbate the Fund’s exposure to volatile markets. The Fund may also be limited in its ability to execute favorable trades in portfolio securities in response to changes in share prices and fundamentals, and may be forced to dispose of securities under disadvantageous circumstances and at a loss. As the Fund grows in size, these considerations take on increasing significance and may adversely impact performance.

Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies.

U.S. Government Obligations Risk. While U.S. Treasury obligations are backed by the “full faith and credit” of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government.

Derivatives Risk. Losses involving derivative instruments may be substantial, because a relatively small movement in the price of an underlying security, instrument, commodity, currency or index may result in a substantial loss for the Fund. In addition to the potential for increased losses, the use of derivative instruments may lead to increased volatility for the Fund. Derivative investments will typically increase the Fund’s exposure to principal risks to which it is otherwise exposed, and may expose the Fund to additional risks, including correlation risk, counterparty risk, hedging risk, leverage risk and/or liquidity risk.

Convertible Securities Risk. Convertible securities are subject to the usual risks associated with debt securities, such as interest rate risk and credit risk. Convertible securities also react to changes in the value of the common stock into which they convert, and are thus subject to market risk. The Fund may also be forced to convert a convertible security at an inopportune time, which may decrease the Fund’s return.

Forward Commitments on Mortgage-Backed Securities (including Dollar Rolls) Risk. When purchasing mortgage-backed securities in the “to be announced” (TBA) market (MBS TBAs), the seller agrees to deliver mortgage-backed securities for an agreed upon price on an agreed upon date, but may make no guarantee as to the specific securities to be delivered. In lieu of taking delivery of mortgage-backed securities, the Fund could enter into dollar rolls, which are transactions in which the Fund sells securities to a counterparty and simultaneously agrees to purchase those or similar securities in the future at a predetermined price. Dollar rolls involve the risk that the market value of the securities the Fund is obligated to repurchase may decline below the repurchase price, or that the counterparty may default on its obligations. These transactions may also increase the Fund’s portfolio turnover rate. If the Fund reinvests the proceeds of the security sold, the Fund will also be subject to the risk that the investments purchased with such proceeds will decline in value (a form of leverage risk). MBS TBAs and dollar rolls are subject to counterparty risk (the risk that the counterparty to the instrument will not perform or be able to perform in accordance with the terms of the instrument).

Mortgage- and Other Asset-Backed Securities Risk. The value of any mortgage-backed and other asset-backed securities held by the Fund may be affected by, among other things, changes or perceived changes in: interest rates; factors concerning the interests in and structure of the issuer or the originator of the mortgages or other assets; the creditworthiness of the entities that provide any supporting letters of credit, surety bonds or other credit enhancements; or the market's assessment of the quality of underlying assets. Payment of principal and interest on some mortgage-backed securities (but not the market value of the securities themselves) may be guaranteed by the full faith and credit of a particular U.S. Government agency, authority, enterprise or instrumentality, and some, but not all, are also insured or guaranteed by the U.S. Government. Mortgage-backed securities issued by non-governmental issuers (such as commercial banks, savings and loan institutions, private mortgage insurance companies, mortgage bankers and other secondary market issuers) may entail greater risk than obligations guaranteed by the U.S. Government. Mortgage- and other asset-backed securities are subject to prepayment risk, which is the possibility that the underlying mortgage or other asset may be refinanced or prepaid prior to maturity during periods of declining or low interest rates, causing the Fund to have to reinvest the money received in securities that have lower yields. Rising or high interest rates tend to extend the duration of mortgage- and other asset-backed securities, making their prices more volatile and more sensitive to changes in interest rates.

Stripped Securities Risk. Stripped securities are the separate income or principal components of debt securities. These securities are particularly sensitive to changes in interest rates, and therefore subject to greater fluctuations in price than typical interest bearing debt securities.

Prepayment and Extension Risk. Prepayment and extension risk is the risk that a bond or other security or investment might, in the case of prepayment risk, be called or otherwise converted, prepaid or redeemed before maturity and, in the case of extension risk, the investment might not be called as expected, and the portfolio managers may not be able to invest the proceeds in other investments providing as high a level of income, resulting in a reduced yield to the Fund. In the case of mortgage- or asset-backed securities, as interest rates decrease or spreads narrow, the likelihood of prepayment increases. Conversely, extension risk is the risk that an unexpected rise in interest rates will extend the life of a mortgage- or asset-backed security beyond the prepayment time. If the Fund’s investments are locked in at a lower interest rate for a longer period of time, the portfolio managers may be unable to capitalize on securities with higher interest rates or wider spreads.

Reinvestment Risk. Reinvestment risk is the risk that the Fund will not be able to reinvest income or principal at the same return it is currently earning.

Depositary Receipts Risk. Depositary receipts are receipts issued by a bank or trust company reflecting ownership of underlying securities issued by foreign companies. Some foreign securities are traded in the form of American Depositary Receipts (ADRs). Depositary receipts involve risks similar to the risks associated with investments in foreign securities, including those associated with the particular country, which may be related to the particular political, regulatory, economic, social and other conditions or events occurring in the country and fluctuations in its currency, as well as market risk tied to the underlying foreign company. In addition, ADR holders may have limited voting rights, may not have the same rights afforded typical company stockholders in the event of a corporate action such as an acquisition, merger or rights offering and may experience difficulty in receiving company stockholder communications.

Derivatives Risk/Futures Contracts Risk. The loss that may be incurred in entering into futures contracts may exceed the amount of the premium paid and may be potentially unlimited. Futures markets are highly volatile and the use of futures may increase the volatility of the Fund’s NAV. Additionally, as a result of the low collateral deposits normally involved in futures trading, a relatively small price movement in a futures contract may result in substantial losses for the Fund. Futures contracts may be illiquid. Furthermore, exchanges may limit fluctuations in futures contract prices during a trading session by imposing a maximum permissible price movement on each futures contract. The Fund may be disadvantaged if it is prohibited from executing a trade outside the daily permissible price movement. Futures contracts executed on foreign exchanges may not provide the same protection as U.S. exchanges. These transactions involve additional risks, including counterparty risk, hedging risk and pricing risk.

Changing Distribution Level Risk. The amount of the distributions paid by the Fund will vary and generally depends on the amount of interest income and/or dividends received by the Fund on the securities it holds. The Fund may not be able to pay distributions or may have to reduce its distribution level if the interest income and/or dividends the Fund receives from its investments decline.

Rule 144A Securities Risk. The Fund may invest significantly in privately placed “Rule 144A” securities that are determined to be liquid in accordance with procedures adopted by the Fund’s Board. However, an insufficient number of qualified institutional buyers interested in purchasing Rule 144A securities at a particular time could affect adversely the marketability of such securities and the Fund might be unable to dispose of such securities promptly or at reasonable prices. Accordingly, even if determined to be liquid, the Fund’s holdings of Rule 144A securities may increase the level of Fund illiquidity if eligible buyers become uninterested in buying them at a particular time. Issuers of Rule 144A securities are required to furnish information to potential investors upon request. However, the required disclosure is much less extensive than that required of public companies and is not publicly available since it is not filed with the SEC. Further, issuers of Rule 144A securities can require recipients of the information (such as the Fund) to agree contractually to keep the information confidential, which could also adversely affect the Fund’s ability to dispose of the security.

Frequent Trading Risk. The portfolio managers may actively and frequently trade investments in the Fund's portfolio to carry out its investment strategies. Frequent trading of investments increases the possibility that the Fund, as relevant, will realize taxable capital gains (including short-term capital gains, which are generally taxable to shareholders at higher rates than long-term capital gains for U.S. federal income tax purposes), which could reduce the Fund's after-tax return. Frequent trading can also mean higher brokerage and other transaction costs, which could reduce the Fund's return. The trading costs and tax effects associated with portfolio turnover may adversely affect the Fund’s performance.

Select Portfolio Risk. Because the Fund may invest in a limited number of companies, the Fund as a whole is subject to greater risk of loss if any of its portfolio securities decline in price. In addition, the Fund’s holdings and weightings will diverge significantly from its primary benchmark’s holdings and weightings and the Fund may therefore experience greater risk and volatility relative to the benchmark. Because the Fund may invest in more than one company concentrated in a similar industry, sector or geographic region, the Fund may be even more concentrated than the number of companies it may hold would suggest.

Index Risk. The Fund's value will generally decline when the performance of its targeted index declines. In addition, because the Fund may not hold all issues included in its index, it may not always be fully invested. The Fund also bears advisory, administrative and other expenses and transaction costs in trading securities, which the index does not bear. Accordingly, the Fund's performance will likely fail to match the performance of its targeted index, after taking expenses into account. It is not possible to invest directly in an index.

Highly Leveraged Transactions Risk. The loans or other securities in which the Fund invests may include highly leveraged transactions whereby the borrower assumes large amounts of debt in order to have the financial resources to attempt to achieve its business objectives. Loans or securities that are part of highly leveraged transactions involve a greater risk (including default and bankruptcy) than other investments.

Issuer Risk. An issuer in which the Fund invests or to which it has exposure may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors.

Performance Information

The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with those of the S&P 500^® Index, the Fund’s primary benchmark for equity securities, the Barclays U.S. Aggregate Bond Index, the Fund’s primary benchmark for debt securities, the Lipper Flexible Portfolio Funds Index and a 50/50 Blended Benchmark. The S&P 500^® Index tracks the performance of 500 widely held, large-capitalization U.S. stocks. The Barclays U.S. Aggregate Bond Index is a market value-weighted index that tracks the daily price, coupon, pay-downs, and total return performance of fixed-rate, publicly placed, dollar-denominated, and non-convertible investment grade debt issues with at least $250 million par amount outstanding and with at least one year to final maturity. The Lipper Flexible Portfolio Funds Index is an equal-weighted index of the 30 largest mutual funds within the Flexible Portfolio fund classification, as defined by Lipper, and shows how the Fund’s performance compares with the returns of an index of funds with similar investment objectives. The 50/50 Blended Benchmark was established by the Investment Manager to show how the Fund’s performance compares to an equally weighted custom composite of the Fund’s primary equity and primary debt benchmarks, the S&P 500^® Index and the Barclays U.S. Aggregate Bond Index, respectively. The percentage of the Fund’s assets allocated to underlying stock and bond Portfolio Funds will vary, and accordingly the composition of the Fund’s portfolio will not always reflect the composition of the 50/50 Blended Benchmark.

The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities.

The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-deferred accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes.

The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.

Year by Year Total Return (%)
as of December 31 Each Year

Best and Worst Quarterly Returns
During the Period Shown in the Bar Chart

Best                            2nd Quarter 2009                            19.33%

Worst                         4th Quarter 2008                            -19.26%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2014)

Average Annual Total Returns Columbia Thermostat Fund	Share Class Inception Date	1 Year	5 Years	10 Years
Class Z	Sep. 25, 2002	5.57%	10.09%	6.55%
Class Z returns after taxes on distributions	Sep. 25, 2002	4.15%	8.98%	5.13%
Class Z returns after taxes on distributions and sale of Fund shares	Sep. 25, 2002	3.34%	7.70%	4.83%
Class A	Mar. 03, 2003	(0.75%)	8.54%	5.66%
Class B	Mar. 03, 2003	(0.17%)	9.00%	5.73%
Class C	Mar. 03, 2003	3.50%	9.00%	5.49%
Class R4	Nov. 08, 2012	5.61%	10.09%	6.55%
Class R5	Nov. 08, 2012	5.62%	10.11%	6.56%
Class Y	Nov. 08, 2012	5.68%	10.14%	6.57%
S&P 500® Index (reflects no deductions for fees, expenses or taxes)		13.69%	15.45%	7.67%
Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)		5.97%	4.45%	4.71%
Lipper Flexible Portfolio Funds Index (reflects no deductions for taxes)		4.31%	8.80%	6.11%
50/50 Blended Benchmark (an equally weighted custom composite of the Fund's primary benchmarks for equity and debt securities, established by the Investment Manager; reflects no deductions for fees, expenses or taxes)		9.85%	10.09%	6.48%

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] This charge decreases over time.

[3] This charge applies to redemptions within one year after purchase, with certain limited exceptions.

[1] "Total annual Fund operating expenses" include acquired fund (Portfolio Fund) fees and expenses (expenses the Fund incurs indirectly through its investments in other funds) and may be higher than "Total Net Expenses" shown in the Financial Highlights section of this prospectus because "Total Net Expenses" do not include Portfolio Fund (acquired fund) fees and expenses.

[2] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund's investment in the Portfolio Funds (acquired funds)), do not exceed the annual rates of 0.50% for Class A shares, 1.00% for Class B shares, 1.25% for Class C shares, 0.25% for Class R4 shares, 0.24% for Class R5 shares, 0.19% for Class Y shares and 0.25% for Class Z shares, through April 30, 2016. This arrangement may only be modified or amended with approval from all parties to the arrangement, including the Fund and the Investment Manager.

[1] Year to Date return as of March 31, 2015: 1.50%