Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2020
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. 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 20 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	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, 2021
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 91% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	91.00%
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 20 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 fees paid by the Fund.
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 (including the amount of any borrowings for investment purposes) in U.S. companies. 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 Investment Manager from time to time emphasizes one or more sectors in selecting the Fund’s investments. 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 risks, including those described below, among others. 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. Market Risk. The Fund may incur losses due to declines in the value of one or more securities in which it invests. These declines may be due to factors affecting a particular issuer, or the result of, among other things, political, regulatory, market, economic or social developments affecting the market(s) generally. In addition, turbulence in the financial markets generally and reduced liquidity in the equity, credit and/or fixed income markets more specifically may negatively affect many issuers, which could adversely affect the Fund, including by causing difficulty in pricing hard-to-value assets in thinly traded and closed markets, significant redemptions and operational challenges. Global economies and financial markets are increasingly interconnected, and conditions and events in one country, region, financial market or industry sector may adversely impact issuers in a different country, region, financial market or industry sector. These risks may be magnified if certain events or developments adversely interrupt the global supply chain; in these and other circumstances, such risks might affect companies worldwide. As a result, local, regional or global events such as terrorism, war, natural disasters, disease/virus outbreaks and epidemics or other public health crises, recessions, depressions or other events – or the potential for such events – could have a significant negative impact on global economic and market conditions. The public health crisis caused by the novel coronavirus disease known as COVID-19 has become a pandemic that has resulted in, and may continue to result in, significant global economic and market volatility arising from disruptions in market access, resource availability, facilities operations, imposition of tariffs, export controls and supply chains, among other factors. These and related societal disruptions have been caused or exacerbated by, and may continue to be caused or exacerbated by, quarantines and travel restrictions, workforce displacement and loss in human and other resources. There is significant uncertainty surrounding the magnitude, duration, reach, costs and other effects of the COVID-19 global pandemic, including actions that have been or could be taken by governmental authorities or other third parties. The impacts, as well as the uncertainty over impacts yet to unfold, of COVID-19 – and any other infectious illness outbreaks, epidemics, pandemics or other public health crises that may arise in the future – could negatively affect global economies and markets in ways that cannot necessarily be foreseen. In addition, the impact of infectious illness outbreaks, and epidemics, pandemics and other public health crises in emerging market countries may be greater due to generally less established healthcare systems, governments and financial markets. Public health crises caused by the COVID-19 pandemic may exacerbate other pre-existing political, social and economic risks in certain countries or globally. The disruptions caused by COVID-19 could prevent the Investment Manager from executing advantageous investment decisions for the Fund in a timely manner and could negatively impact the Fund’s ability to achieve its investment objective. Any such event(s) could have a significant adverse impact on the value and risk profile of the Fund. 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 of an issuer 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, military confrontations, war, terrorism, disease/virus outbreaks and epidemics or other events, conditions and factors. 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 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. Health Care Sector. The Fund may be more susceptible to the particular risks that may affect companies in the health care sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the health care sector are subject to certain risks, including restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, and the rising cost of medical products and services (especially for companies dependent upon a relatively limited number of products or services), among others. Performance of such companies may be affected by factors including, government regulation, obtaining and protecting patents (or the failure to do so), product liability and other similar litigation as well as product obsolescence. Information Technology Sector. The Fund may be more susceptible to the particular risks that may affect companies in the information technology sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the information technology sector are subject to certain risks, including the risk that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. Performance of such companies may be affected by factors including obtaining and protecting patents (or the failure to do so) and significant competitive pressures, including aggressive pricing of their products or services, new market entrants, competition for market share and short product cycles due to an accelerated rate of technological developments. Such competitive pressures may lead to limited earnings and/or falling profit margins. As a result, the value of their securities may fall or fail to rise. In addition, many information technology sector companies have limited operating histories and prices of these companies’ securities historically have been more volatile than other securities, especially over the short term.
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	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 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 2000 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. 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 2000 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	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 2019                                                         16.90% Worst                                                        3rd Quarter 2011                                                       -22.20%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2019)
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.
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	0.92%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.27%	[2]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.44%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.03%)	[3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.41%
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	$ 710
3 years	rr_ExpenseExampleYear03	1,002
5 years	rr_ExpenseExampleYear05	1,314
10 years	rr_ExpenseExampleYear10	2,198
1 year	rr_ExpenseExampleNoRedemptionYear01	710
3 years	rr_ExpenseExampleNoRedemptionYear03	1,002
5 years	rr_ExpenseExampleNoRedemptionYear05	1,314
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 2,198
1 Year	rr_AverageAnnualReturnYear01	23.32%
5 Years	rr_AverageAnnualReturnYear05	9.78%
10 Years	rr_AverageAnnualReturnYear10	11.66%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn USA | 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	0.92%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.27%	[2]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.19%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.03%)	[3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.16%
1 year	rr_ExpenseExampleYear01	$ 118
3 years	rr_ExpenseExampleYear03	375
5 years	rr_ExpenseExampleYear05	651
10 years	rr_ExpenseExampleYear10	1,441
1 year	rr_ExpenseExampleNoRedemptionYear01	118
3 years	rr_ExpenseExampleNoRedemptionYear03	375
5 years	rr_ExpenseExampleNoRedemptionYear05	651
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,441
1 Year	rr_AverageAnnualReturnYear01	31.27%
5 Years	rr_AverageAnnualReturnYear05	11.36%
10 Years	rr_AverageAnnualReturnYear10	12.62%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
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%	[4]
Management fees	rr_ManagementFeesOverAssets	0.92%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.27%	[2]
Total annual Fund operating expenses	rr_ExpensesOverAssets	2.19%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.03%)	[3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	2.16%
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	$ 319
3 years	rr_ExpenseExampleYear03	682
5 years	rr_ExpenseExampleYear05	1,172
10 years	rr_ExpenseExampleYear10	2,521
1 year	rr_ExpenseExampleNoRedemptionYear01	219
3 years	rr_ExpenseExampleNoRedemptionYear03	682
5 years	rr_ExpenseExampleNoRedemptionYear05	1,172
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 2,521
1 Year	rr_AverageAnnualReturnYear01	29.02%
5 Years	rr_AverageAnnualReturnYear05	10.29%
10 Years	rr_AverageAnnualReturnYear10	11.52%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn USA | 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	0.92%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.27%	[2]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.19%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.03%)	[3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.16%
1 year	rr_ExpenseExampleYear01	$ 118
3 years	rr_ExpenseExampleYear03	375
5 years	rr_ExpenseExampleYear05	651
10 years	rr_ExpenseExampleYear10	1,441
1 year	rr_ExpenseExampleNoRedemptionYear01	118
3 years	rr_ExpenseExampleNoRedemptionYear03	375
5 years	rr_ExpenseExampleNoRedemptionYear05	651
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,441
2010	rr_AnnualReturn2010	23.16%	[5]
2011	rr_AnnualReturn2011	(4.95%)	[5]
2012	rr_AnnualReturn2012	18.98%	[5]
2013	rr_AnnualReturn2013	32.72%	[5]
2014	rr_AnnualReturn2014	3.61%	[5]
2015	rr_AnnualReturn2015	(1.36%)	[5]
2016	rr_AnnualReturn2016	13.00%	[5]
2017	rr_AnnualReturn2017	19.44%	[5]
2018	rr_AnnualReturn2018	(1.98%)	[5]
2019	rr_AnnualReturn2019	31.28%	[5]
Year to Date Return, Label	rr_YearToDateReturnLabel	Year to Date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2020
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	(27.03%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2019
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	16.90%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(22.20%)
1 Year	rr_AverageAnnualReturnYear01	31.28%
5 Years	rr_AverageAnnualReturnYear05	11.37%
10 Years	rr_AverageAnnualReturnYear10	12.62%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 04, 1996
Columbia Acorn USA | 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	0.92%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.21%	[2]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.13%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.05%)	[3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.08%
1 year	rr_ExpenseExampleYear01	$ 110
3 years	rr_ExpenseExampleYear03	354
5 years	rr_ExpenseExampleYear05	617
10 years	rr_ExpenseExampleYear10	1,370
1 year	rr_ExpenseExampleNoRedemptionYear01	110
3 years	rr_ExpenseExampleNoRedemptionYear03	354
5 years	rr_ExpenseExampleNoRedemptionYear05	617
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,370
1 Year	rr_AverageAnnualReturnYear01	31.41%
5 Years	rr_AverageAnnualReturnYear05	11.48%
10 Years	rr_AverageAnnualReturnYear10	12.69%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn USA | 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	0.92%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.16%	[2]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.08%
Less: Fee waivers and/or expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.04%)	[3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	rr_NetExpensesOverAssets	1.04%
1 year	rr_ExpenseExampleYear01	$ 106
3 years	rr_ExpenseExampleYear03	340
5 years	rr_ExpenseExampleYear05	592
10 years	rr_ExpenseExampleYear10	1,314
1 year	rr_ExpenseExampleNoRedemptionYear01	106
3 years	rr_ExpenseExampleNoRedemptionYear03	340
5 years	rr_ExpenseExampleNoRedemptionYear05	592
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,314
1 Year	rr_AverageAnnualReturnYear01	31.45%
5 Years	rr_AverageAnnualReturnYear05	11.52%
10 Years	rr_AverageAnnualReturnYear10	12.72%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn USA | returns after taxes on distributions | Class Inst
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	27.80%
5 Years	rr_AverageAnnualReturnYear05	5.21%
10 Years	rr_AverageAnnualReturnYear10	8.66%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 04, 1996
Columbia Acorn USA | returns after taxes on distributions and sale of Fund shares | Class Inst
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	20.53%
5 Years	rr_AverageAnnualReturnYear05	7.51%
10 Years	rr_AverageAnnualReturnYear10	9.48%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 04, 1996
Columbia Acorn USA | Russell 2000 Growth Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	28.48%
5 Years	rr_AverageAnnualReturnYear05	9.34%
10 Years	rr_AverageAnnualReturnYear10	13.01%

[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 fees paid by the Fund.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through April 30, 2021, 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 1.41% for Class A shares, 1.16% for Class Adv shares, 2.16% for Class C shares, 1.16% for Class Inst shares, 1.08% for Class Inst2 shares and 1.04% 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. The fee waivers and/or expense reimbursements shown in the table also reflect the contractual agreement of the Fund’s transfer agent, Columbia Management Investment Services Corp. (the Transfer Agent), to waive a portion of its fees through April 30, 2021, such that the Fund’s transfer agency fees do not exceed the annual rates of 0.04% of the average daily net assets of Class Inst2 shares and 0.00% of the average daily net assets of Class Inst3 shares.

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

[5] Year to Date return as of March 31, 2020: -27.03%