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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, hold and sell shares of the Fund.
You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.
You may be required to pay such brokerage commissions and other fees to financial intermediaries when transacting in any class of Fund shares, including those that do not assess any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution. Such brokerage commissions and other fees are set by the financial intermediary. 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 25 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, 2022
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 94% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 94.00%
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 25 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
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.
Effective April 1, 2021, Class C shares generally automatically convert to Class A shares of the same Fund on approximately the 8-year anniversary of the Class C shares purchase date (Class C Shares 8-Year Conversion Policy). Class C shares’ 10-year cost examples below reflect the Class C Shares 8-Year Conversion Policy.
 
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 invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations generally in the range of market capitalizations in the Russell 2000 Growth Index, the Fund's benchmark, (the Index) at the time of purchase (between $49.3 million and $18.2 billion as of March 31, 2021). The market capitalization range and composition of companies in the Index are subject to change. As such, the size of the companies in which the Fund invests may change. As long as an investment continues to meet the Fund’s other investment criteria, the Fund may continue to hold and make new investments in a security even if the company’s market capitalization grows beyond the market capitalization of the largest company within the Index or falls below the market capitalization of the smallest company within the Index.
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 may invest up to 20% of its
total assets in foreign securities. The Fund may invest directly in foreign securities or indirectly through depositary receipts. Depositary receipts are receipts issued by a bank or trust company reflecting ownership of underlying securities issued by foreign 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.
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.
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 COVID-19 pandemic 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.
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.
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.
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 is 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 is 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. Some companies in the information technology sector are facing increased government and regulatory scrutiny and may be subject to adverse government or regulatory action, which could negatively impact the value of their securities.
Depositary Receipts Risk.
Depositary receipts are receipts issued by a bank or trust company reflecting ownership of underlying securities issued by foreign companies. Some foreign securities are traded in the form of American Depositary Receipts and/or Global Depositary Receipts. Depositary receipts involve risks similar to the risks associated with investments in foreign securities, including those associated with investing in the particular country of an issuer, which may be related to the particular political, regulatory, economic, social and other conditions or events, including, for example, military confrontations, war, terrorism and disease/virus outbreaks and epidemics, occurring in the country and fluctuations in such country’s currency, as well as market risk tied to the underlying foreign company. In addition, holders of depositary receipts may have limited voting rights, may not have the same rights afforded to stockholders of a typical domestic company in the event of a corporate action, such as an acquisition, merger or rights offering, and may experience difficulty in receiving company stockholder communications. There is no guarantee that a financial institution will continue to sponsor a depositary receipt, or that a depositary receipt will continue to trade on an exchange, either of which could adversely affect the liquidity, availability and pricing of the depositary receipt. Changes in foreign currency exchange rates will affect the value of depositary receipts and, therefore, may affect the value of your investment in the Fund.
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, terrorism and disease/virus outbreaks and epidemics), 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.
Foreign Currency Risk.
The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.
Risk Lose Money [Text] rr_RiskLoseMoney There is no assurance that the Fund will achieve its investment objective and you may lose money.
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 2nd Quarter 2020 26.69% Worst 1st Quarter 2020 -27.03%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2020)
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 0.93%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.26%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.44%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.04%) [2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.40%
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 $ 709
3 years rr_ExpenseExampleYear03 1,001
5 years rr_ExpenseExampleYear05 1,313
10 years rr_ExpenseExampleYear10 2,197
1 year rr_ExpenseExampleNoRedemptionYear01 709
3 years rr_ExpenseExampleNoRedemptionYear03 1,001
5 years rr_ExpenseExampleNoRedemptionYear05 1,313
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,197
1 Year rr_AverageAnnualReturnYear01 16.62%
5 Years rr_AverageAnnualReturnYear05 14.92%
10 Years rr_AverageAnnualReturnYear10 11.74%
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 0.93%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.26%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.19%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.04%) [2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.15%
1 year rr_ExpenseExampleYear01 $ 117
3 years rr_ExpenseExampleYear03 374
5 years rr_ExpenseExampleYear05 650
10 years rr_ExpenseExampleYear10 1,440
1 year rr_ExpenseExampleNoRedemptionYear01 117
3 years rr_ExpenseExampleNoRedemptionYear03 374
5 years rr_ExpenseExampleNoRedemptionYear05 650
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,440
1 Year rr_AverageAnnualReturnYear01 24.08%
5 Years rr_AverageAnnualReturnYear05 16.59%
10 Years rr_AverageAnnualReturnYear10 12.70%
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% [3]
Management fees rr_ManagementFeesOverAssets 0.93%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.26%
Total annual Fund operating expenses rr_ExpensesOverAssets 2.19%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.04%) [2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 2.15%
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 $ 318
3 years rr_ExpenseExampleYear03 681
5 years rr_ExpenseExampleYear05 1,171
10 years rr_ExpenseExampleYear10 2,331
1 year rr_ExpenseExampleNoRedemptionYear01 218
3 years rr_ExpenseExampleNoRedemptionYear03 681
5 years rr_ExpenseExampleNoRedemptionYear05 1,171
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,331
1 Year rr_AverageAnnualReturnYear01 21.79%
5 Years rr_AverageAnnualReturnYear05 15.45%
10 Years rr_AverageAnnualReturnYear10 11.60%
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 0.93%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.26%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.19%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.04%) [2]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.15%
1 year rr_ExpenseExampleYear01 $ 117
3 years rr_ExpenseExampleYear03 374
5 years rr_ExpenseExampleYear05 650
10 years rr_ExpenseExampleYear10 1,440
1 year rr_ExpenseExampleNoRedemptionYear01 117
3 years rr_ExpenseExampleNoRedemptionYear03 374
5 years rr_ExpenseExampleNoRedemptionYear05 650
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,440
2011 rr_AnnualReturn2011 (4.95%) [4]
2012 rr_AnnualReturn2012 18.98% [4]
2013 rr_AnnualReturn2013 32.72% [4]
2014 rr_AnnualReturn2014 3.61% [4]
2015 rr_AnnualReturn2015 (1.36%) [4]
2016 rr_AnnualReturn2016 13.00% [4]
2017 rr_AnnualReturn2017 19.44% [4]
2018 rr_AnnualReturn2018 (1.98%) [4]
2019 rr_AnnualReturn2019 31.28% [4]
2020 rr_AnnualReturn2020 24.04% [4]
Year to Date Return, Label rr_YearToDateReturnLabel Year to Date return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2021
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 5.75%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 26.69%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (27.03%)
1 Year rr_AverageAnnualReturnYear01 24.04%
5 Years rr_AverageAnnualReturnYear05 16.59%
10 Years rr_AverageAnnualReturnYear10 12.70%
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 0.93%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.14%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.06%) [2]
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 356
5 years rr_ExpenseExampleYear05 622
10 years rr_ExpenseExampleYear10 1,381
1 year rr_ExpenseExampleNoRedemptionYear01 110
3 years rr_ExpenseExampleNoRedemptionYear03 356
5 years rr_ExpenseExampleNoRedemptionYear05 622
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,381
1 Year rr_AverageAnnualReturnYear01 24.10%
5 Years rr_AverageAnnualReturnYear05 16.69%
10 Years rr_AverageAnnualReturnYear10 12.77%
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 0.93%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.16%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.09%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.05%) [2]
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 342
5 years rr_ExpenseExampleYear05 596
10 years rr_ExpenseExampleYear10 1,324
1 year rr_ExpenseExampleNoRedemptionYear01 106
3 years rr_ExpenseExampleNoRedemptionYear03 342
5 years rr_ExpenseExampleNoRedemptionYear05 596
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,324
1 Year rr_AverageAnnualReturnYear01 24.16%
5 Years rr_AverageAnnualReturnYear05 16.74%
10 Years rr_AverageAnnualReturnYear10 12.81%
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 22.53%
5 Years rr_AverageAnnualReturnYear05 11.40%
10 Years rr_AverageAnnualReturnYear10 8.60%
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 14.97%
5 Years rr_AverageAnnualReturnYear05 11.69%
10 Years rr_AverageAnnualReturnYear10 9.11%
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 34.63%
5 Years rr_AverageAnnualReturnYear05 16.36%
10 Years rr_AverageAnnualReturnYear10 13.48%
[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
[2] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through April 30, 2022, 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 1.40% for Class A shares, 1.15% for Class Adv shares, 2.15% for Class C shares, 1.15% 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, 2022, 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. This arrangement may be terminated at the sole discretion of the Fund’s Board of Trustees.
[3] This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.
[4] Year to Date return as of March 31, 2021: 5.75%