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%