Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2019
Columbia Acorn Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY OF THE FUND
Objective [Heading]	rr_ObjectiveHeading	<b>Investment Objective</b>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Columbia Acorn® Fund (the Fund) seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	<b>Fees and Expenses of the Fund</b>
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. An investor transacting in a class of Fund shares without any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution may be required to pay a commission to the financial intermediary for effecting such transactions. Such commission rates are set by the financial intermediary and are not reflected in the tables or the example below. 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 is available about these and other sales charge discounts and waivers from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 23 of the Fund’s prospectus, in Appendix A to the prospectus beginning on page A-1 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	<b>Shareholder Fees (fees paid directly from your investment) </b>
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	<b>Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment) </b>
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 30, 2020
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	<b>Portfolio Turnover</b>
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 66% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	66.00%
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 is available about these and other sales charge discounts and waivers from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 23 of the Fund’s prospectus, in Appendix A to the prospectus beginning on page A-1 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 Restated to Reflect Current [Text]	rr_ExpensesRestatedToReflectCurrent	Other expenses have been restated to reflect current transfer agency fees paid by the Fund.
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 the ratio of expenses to average net assets shown in the Financial Highlights section of this prospectus because the ratio of expenses to average net assets does not include acquired fund fees and expenses.
Expense Example [Heading]	rr_ExpenseExampleHeading	<b>Example</b>
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	<b>Principal Investment Strategies</b>
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal circumstances, the Fund (i) 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 (“Focus Stocks”) and (ii) may also invest in companies with market capitalizations above $5 billion, provided that immediately after that investment a majority of the Fund’s net assets would be invested in Focus Stocks. The Fund may continue to hold, and make additional investments in, Focus Stocks whose market capitalizations have grown to exceed $5 billion, regardless of whether the Fund’s investments in Focus Stocks are a majority of the Fund’s net assets. Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of small- and mid-sized companies, 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	<b>Principal Risks</b>
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	An investment in the Fund involves risks, 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. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. 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 and/or strategies. Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-cap companies often involve greater risks than investments in larger, more established 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 may negatively affect the Fund’s performance. Underperformance 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. 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. 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. 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 political, regulatory, economic, social, diplomatic and other conditions or events (including, for example, military confrontations, war and terrorism), 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. In addition, foreign governments may impose withholding or other taxes on the Fund’s income, capital gains or proceeds from the disposition of foreign securities, which could reduce the Fund’s return on such securities. 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 have an active trading market 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 and may affect the value of your investment in the Fund. 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. 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 or, conversely, if it faces significant redemption pressure, 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 within one or more economic sectors. Companies in the same 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 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.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	<b>Performance Information</b>
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 Inst 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 2500 Growth Index. The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Inst 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 in effect during the period indicated in the table 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-advantaged accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Inst 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 columbiathreadneedleus.com.
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 Inst 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 2500 Growth Index.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800.345.6611
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	columbiathreadneedleus.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	<b>The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.</b>
Bar Chart [Heading]	rr_BarChartHeading	<b>Year by Year Total Return (%)<br/> 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 2018                                                      -19.76%
Performance Table Heading	rr_PerformanceTableHeading	<b>Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2018)</b>
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 in effect during the period indicated in the table 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-advantaged 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 Inst 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	0.67%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.18%	[2]
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.02%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.12%	[3]
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[4]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.11%
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	$ 682
3 years	rr_ExpenseExampleYear03	910
5 years	rr_ExpenseExampleYear05	1,156
10 years	rr_ExpenseExampleYear10	1,859
1 year	rr_ExpenseExampleNoRedemptionYear01	682
3 years	rr_ExpenseExampleNoRedemptionYear03	910
5 years	rr_ExpenseExampleNoRedemptionYear05	1,156
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,859
1 Year	rr_AverageAnnualReturnYear01	(10.68%)
5 Years	rr_AverageAnnualReturnYear05	3.92%
10 Years	rr_AverageAnnualReturnYear10	11.96%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn Fund | Class Adv
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	0.67%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.18%	[2]
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.02%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.87%	[3]
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[4]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	0.86%
1 year	rr_ExpenseExampleYear01	$ 88
3 years	rr_ExpenseExampleYear03	277
5 years	rr_ExpenseExampleYear05	481
10 years	rr_ExpenseExampleYear10	1,072
1 year	rr_ExpenseExampleNoRedemptionYear01	88
3 years	rr_ExpenseExampleNoRedemptionYear03	277
5 years	rr_ExpenseExampleNoRedemptionYear05	481
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,072
1 Year	rr_AverageAnnualReturnYear01	(5.00%)
5 Years	rr_AverageAnnualReturnYear05	5.38%
10 Years	rr_AverageAnnualReturnYear10	12.90%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
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%	[5]
Management fees	rr_ManagementFeesOverAssets	0.67%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.18%	[2]
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.02%
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.87%	[3]
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[4]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.86%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.
1 year	rr_ExpenseExampleYear01	$ 289
3 years	rr_ExpenseExampleYear03	587
5 years	rr_ExpenseExampleYear05	1,010
10 years	rr_ExpenseExampleYear10	2,190
1 year	rr_ExpenseExampleNoRedemptionYear01	189
3 years	rr_ExpenseExampleNoRedemptionYear03	587
5 years	rr_ExpenseExampleNoRedemptionYear05	1,010
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 2,190
1 Year	rr_AverageAnnualReturnYear01	(6.58%)
5 Years	rr_AverageAnnualReturnYear05	4.39%
10 Years	rr_AverageAnnualReturnYear10	11.79%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn Fund | Class Inst
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	0.67%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.18%	[2]
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.02%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.87%	[3]
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[4]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	0.86%
1 year	rr_ExpenseExampleYear01	$ 88
3 years	rr_ExpenseExampleYear03	277
5 years	rr_ExpenseExampleYear05	481
10 years	rr_ExpenseExampleYear10	1,072
1 year	rr_ExpenseExampleNoRedemptionYear01	88
3 years	rr_ExpenseExampleNoRedemptionYear03	277
5 years	rr_ExpenseExampleNoRedemptionYear05	481
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,072
2009	rr_AnnualReturn2009	39.65%	[6]
2010	rr_AnnualReturn2010	26.00%	[6]
2011	rr_AnnualReturn2011	(4.61%)	[6]
2012	rr_AnnualReturn2012	17.93%	[6]
2013	rr_AnnualReturn2013	30.90%	[6]
2014	rr_AnnualReturn2014	0.82%	[6]
2015	rr_AnnualReturn2015	(1.57%)	[6]
2016	rr_AnnualReturn2016	10.39%	[6]
2017	rr_AnnualReturn2017	25.24%	[6]
2018	rr_AnnualReturn2018	(5.09%)	[6]
Year to Date Return, Label	rr_YearToDateReturnLabel	Year to Date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2019
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	16.56%
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, 2018
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(19.76%)
1 Year	rr_AverageAnnualReturnYear01	(5.09%)
5 Years	rr_AverageAnnualReturnYear05	5.42%
10 Years	rr_AverageAnnualReturnYear10	12.93%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Jun. 10, 1970
Columbia Acorn Fund | Class Inst2
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	0.67%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.14%	[2]
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.02%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.83%	[3]
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[4]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	0.82%
1 year	rr_ExpenseExampleYear01	$ 84
3 years	rr_ExpenseExampleYear03	264
5 years	rr_ExpenseExampleYear05	460
10 years	rr_ExpenseExampleYear10	1,024
1 year	rr_ExpenseExampleNoRedemptionYear01	84
3 years	rr_ExpenseExampleNoRedemptionYear03	264
5 years	rr_ExpenseExampleNoRedemptionYear05	460
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,024
1 Year	rr_AverageAnnualReturnYear01	(5.00%)
5 Years	rr_AverageAnnualReturnYear05	5.45%
10 Years	rr_AverageAnnualReturnYear10	12.95%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn Fund | Class Inst3
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	0.67%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.10%	[2]
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.02%
Total annual Fund operating expenses	rr_ExpensesOverAssets	0.79%	[3]
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[4]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	0.78%
1 year	rr_ExpenseExampleYear01	$ 80
3 years	rr_ExpenseExampleYear03	251
5 years	rr_ExpenseExampleYear05	438
10 years	rr_ExpenseExampleYear10	977
1 year	rr_ExpenseExampleNoRedemptionYear01	80
3 years	rr_ExpenseExampleNoRedemptionYear03	251
5 years	rr_ExpenseExampleNoRedemptionYear05	438
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 977
1 Year	rr_AverageAnnualReturnYear01	(4.98%)
5 Years	rr_AverageAnnualReturnYear05	5.51%
10 Years	rr_AverageAnnualReturnYear10	12.99%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn Fund | returns after taxes on distributions | Class Inst
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(7.76%)
5 Years	rr_AverageAnnualReturnYear05	(0.55%)
10 Years	rr_AverageAnnualReturnYear10	9.29%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Jun. 10, 1970
Columbia Acorn Fund | returns after taxes on distributions and sale of Fund shares | Class Inst
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(0.95%)
5 Years	rr_AverageAnnualReturnYear05	3.55%
10 Years	rr_AverageAnnualReturnYear10	10.43%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Jun. 10, 1970
Columbia Acorn Fund | Russell 2500 Growth Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(7.47%)
5 Years	rr_AverageAnnualReturnYear05	6.19%
10 Years	rr_AverageAnnualReturnYear10	14.76%

[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] Other expenses have been restated to reflect current transfer agency fees paid by the Fund.

[3] “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 the ratio of expenses to average net assets shown in the Financial Highlights section of this prospectus because the ratio of expenses to average net assets does not include acquired fund fees and expenses.

[4] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through April 30, 2020, so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, interest and fees on borrowings, if any) do not exceed the annual rates of 1.11% for Class A shares, 0.86% for Class Adv shares, 1.86% for Class C shares, 0.86% for Class Inst shares, 0.82% for Class Inst2 shares and 0.78% for Class Inst3 shares. This arrangement may only be amended or terminated with approval from the Fund’s Board of Trustees and the Investment Manager.

[5] This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.

[6] Year to Date return as of March 31, 2019: 16.56%