Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2016
Columbia Acorn USA
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY OF THE FUND
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Columbia Acorn USA® (the Fund) seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 17 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 35% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	35.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information about these and other discounts is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 17 of the Fund’s prospectus and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 50,000
Expenses Restated to Reflect Current [Text]	rr_ExpensesRestatedToReflectCurrent	Management fees have been restated to reflect current fees based on current asset levels. Other expenses have been restated and are based on estimated amounts for the Fund’s current fiscal year, taking into consideration changes in the Fund’s net assets.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that: you invest $10,000 in the applicable class of Fund shares for the periods indicated, your investment has a 5% return each year, and the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal circumstances, the Fund invests at least 80% of its net assets (including the amount any borrowings for investment purposes) in U.S. companies. Under normal circumstances, the Fund (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 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 and/or strategies. 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. Small- and Mid-Cap Company Securities Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies. Issuer Risk. An issuer in which the Fund invests may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors. Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within an economic sector. Companies in the same economic sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Generally, the more the Fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.
Risk Lose Money [Text]	rr_RiskLoseMoney	There is no assurance that the Fund will achieve its investment objective and you may lose money.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index. The performance of one or more share classes shown in the Average Annual Total Returns table below includes the Fund’s Class Z share returns (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to the indicated inception date of such share classes. Except for differences in fees and expenses, all share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities. The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-advantaged accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class Z shares and will vary for other share classes. Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares. The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class Z share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns for the periods shown with the Russell 2000 Index. This index measures the performance of the 2,000 smallest companies in the Russell 3000 Index, which represents approximately 10% of the total market capitalization of the Russell 3000 Index.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800.345.6611
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	columbiathreadneedle.com/us
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Year by Year Total Return (%) as of December 31 Each Year
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best and Worst Quarterly Returns During the Period Shown in the Bar Chart Best                                                          3rd Quarter 2009                                                         23.55% Worst                                                        4th Quarter 2008                                                        -27.96%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2015)
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-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 Z shares and will vary for other share classes.
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	Returns after taxes on distributions and sale of Fund shares are higher than before-tax returns for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of Fund shares.
Columbia Acorn USA | Class A
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[1]
Management fees	rr_ManagementFeesOverAssets	0.89%	[2]
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.29%	[3]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.43%
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	$ 712
3 years	rr_ExpenseExampleYear03	1,001
5 years	rr_ExpenseExampleYear05	1,312
10 years	rr_ExpenseExampleYear10	2,190
1 year	rr_ExpenseExampleNoRedemptionYear01	712
3 years	rr_ExpenseExampleNoRedemptionYear03	1,001
5 years	rr_ExpenseExampleNoRedemptionYear05	1,312
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 2,190
1 Year	rr_AverageAnnualReturnYear01	(7.26%)
5 Years	rr_AverageAnnualReturnYear05	7.37%
10 Years	rr_AverageAnnualReturnYear10	5.26%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn USA | Class C
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[4]
Management fees	rr_ManagementFeesOverAssets	0.89%	[2]
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[3]
Total annual Fund operating expenses	rr_ExpensesOverAssets	2.12%
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	$ 315
3 years	rr_ExpenseExampleYear03	664
5 years	rr_ExpenseExampleYear05	1,139
10 years	rr_ExpenseExampleYear10	2,452
1 year	rr_ExpenseExampleNoRedemptionYear01	215
3 years	rr_ExpenseExampleNoRedemptionYear03	664
5 years	rr_ExpenseExampleNoRedemptionYear05	1,139
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 2,452
1 Year	rr_AverageAnnualReturnYear01	(2.92%)
5 Years	rr_AverageAnnualReturnYear05	7.89%
10 Years	rr_AverageAnnualReturnYear10	5.10%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 16, 2000
Columbia Acorn USA | Class I
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.89%	[2]
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.14%	[3]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.03%
1 year	rr_ExpenseExampleYear01	$ 105
3 years	rr_ExpenseExampleYear03	328
5 years	rr_ExpenseExampleYear05	569
10 years	rr_ExpenseExampleYear10	1,259
1 year	rr_ExpenseExampleNoRedemptionYear01	105
3 years	rr_ExpenseExampleNoRedemptionYear03	328
5 years	rr_ExpenseExampleNoRedemptionYear05	569
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,259
1 Year	rr_AverageAnnualReturnYear01	(1.19%)
5 Years	rr_AverageAnnualReturnYear05	9.08%
10 Years	rr_AverageAnnualReturnYear10	6.24%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 27, 2010
Columbia Acorn USA | Class R4
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.89%	[2]
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.32%	[3]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.21%
1 year	rr_ExpenseExampleYear01	$ 123
3 years	rr_ExpenseExampleYear03	384
5 years	rr_ExpenseExampleYear05	665
10 years	rr_ExpenseExampleYear10	1,466
1 year	rr_ExpenseExampleNoRedemptionYear01	123
3 years	rr_ExpenseExampleNoRedemptionYear03	384
5 years	rr_ExpenseExampleNoRedemptionYear05	665
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,466
1 Year	rr_AverageAnnualReturnYear01	(1.36%)
5 Years	rr_AverageAnnualReturnYear05	8.94%
10 Years	rr_AverageAnnualReturnYear10	6.18%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn USA | Class R5
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.89%	[2]
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.19%	[3]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.08%
1 year	rr_ExpenseExampleYear01	$ 110
3 years	rr_ExpenseExampleYear03	343
5 years	rr_ExpenseExampleYear05	595
10 years	rr_ExpenseExampleYear10	1,317
1 year	rr_ExpenseExampleNoRedemptionYear01	110
3 years	rr_ExpenseExampleNoRedemptionYear03	343
5 years	rr_ExpenseExampleNoRedemptionYear05	595
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,317
1 Year	rr_AverageAnnualReturnYear01	(1.23%)
5 Years	rr_AverageAnnualReturnYear05	8.99%
10 Years	rr_AverageAnnualReturnYear10	6.20%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn USA | Class Y
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.89%	[2]
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.14%	[3]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.03%
1 year	rr_ExpenseExampleYear01	$ 105
3 years	rr_ExpenseExampleYear03	328
5 years	rr_ExpenseExampleYear05	569
10 years	rr_ExpenseExampleYear10	1,259
1 year	rr_ExpenseExampleNoRedemptionYear01	105
3 years	rr_ExpenseExampleNoRedemptionYear03	328
5 years	rr_ExpenseExampleNoRedemptionYear05	569
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,259
1 Year	rr_AverageAnnualReturnYear01	(1.23%)
5 Years	rr_AverageAnnualReturnYear05	9.02%
10 Years	rr_AverageAnnualReturnYear10	6.21%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 08, 2012
Columbia Acorn USA | Class Z
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.89%	[2]
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.29%	[3]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.18%
1 year	rr_ExpenseExampleYear01	$ 120
3 years	rr_ExpenseExampleYear03	375
5 years	rr_ExpenseExampleYear05	649
10 years	rr_ExpenseExampleYear10	1,432
1 year	rr_ExpenseExampleNoRedemptionYear01	120
3 years	rr_ExpenseExampleNoRedemptionYear03	375
5 years	rr_ExpenseExampleNoRedemptionYear05	649
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,432
2006	rr_AnnualReturn2006	8.28%	[5]
2007	rr_AnnualReturn2007	3.46%	[5]
2008	rr_AnnualReturn2008	(39.22%)	[5]
2009	rr_AnnualReturn2009	41.49%	[5]
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]
Year to Date Return, Label	rr_YearToDateReturnLabel	Year to Date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2016
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	(6.04%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	23.55%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(27.96%)
1 Year	rr_AverageAnnualReturnYear01	(1.36%)
5 Years	rr_AverageAnnualReturnYear05	8.93%
10 Years	rr_AverageAnnualReturnYear10	6.17%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 04, 1996
Columbia Acorn USA | returns after taxes on distributions | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(7.93%)
5 Years	rr_AverageAnnualReturnYear05	5.87%
10 Years	rr_AverageAnnualReturnYear10	4.49%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 04, 1996
Columbia Acorn USA | returns after taxes on distributions and sale of Fund shares | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	4.75%
5 Years	rr_AverageAnnualReturnYear05	7.14%
10 Years	rr_AverageAnnualReturnYear10	5.02%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 04, 1996
Columbia Acorn USA | Russell 2000 Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(4.41%)
5 Years	rr_AverageAnnualReturnYear05	9.19%
10 Years	rr_AverageAnnualReturnYear10	6.80%

[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] Management fees have been restated to reflect current fees based on current asset levels.

[3] Other expenses have been restated and are based on estimated amounts for the Fund's current fiscal year, taking into consideration changes in the Fund's net assets.

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

[5] Year to Date return as of March 31, 2016: -6.04%