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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName COLUMBIA ACORN TRUST
Prospectus Date rr_ProspectusDate May 01, 2016
Supplement [Text Block] cat4_SupplementTextBlock
Supplement dated June 27, 2016
to the Prospectus, Summary Prospectus and Statement of Additional Information ("SAI") of the following Fund:
Fund Prospectus, Summary Prospectus and SAI Dated
Columbia Acorn Trust  
    Columbia Acorn International SelectSM 5/1/2016
1. The table under the caption "Fees and Expenses of the Fund" in the "Summary of the Fund" section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following:
    
Shareholder Fees (fees paid directly from your investment)
  Class A Class C Classes I, R4,
R5, Y and Z
Maximum sales charge (load) imposed on purchases (as a % of offering price) 5.75% None None
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) 1.00% (a) 1.00% (b) None
    
Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
  Class A Class C Class I Class R4 Class R5 Class Y Class Z
Management fees(c) 0.89% 0.89% 0.89% 0.89% 0.89% 0.89% 0.89%
Distribution and/or service (12b-1) fees 0.25% 1.00% 0.00% 0.00% 0.00% 0.00% 0.00%
Other expenses(d) 0.42% 0.42% 0.30% 0.42% 0.35% 0.30% 0.42%
Total annual Fund operating expenses 1.56% 2.31% 1.19% 1.31% 1.24% 1.19% 1.31%
Less: Fee waivers and/or expense reimbursements(e) (0.16%) (0.16%) (0.17%) (0.16%) (0.17%) (0.17%) (0.16%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements 1.40% 2.15% 1.02% 1.15% 1.07% 1.02% 1.15%
(a) 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.
(b) This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.
(c) Management fees have been restated to reflect current fees based on current asset levels and the contractual agreement of Columbia Wanger Asset Management, LLC (the Investment Manager), effective July 1, 2016, to permanently reduce the investment advisory fee paid by the Fund by 0.05% at all net asset levels.
(d) 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 and changes in the method of allocating transfer agent expenses among Class A, Class C, Class R4 and Class Z shares of the Fund.
(e) Effective July 1, 2016, the Investment Manager has contractually agreed to indefinitely waive fees and reimburse certain expenses of the Fund 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, 2.15% for Class C shares, 1.02% for Class I shares, 1.15% for Class R4 shares, 1.07% for Class R5 shares, 1.02% for Class Y shares and 1.15% for Class Z shares. This arrangement may only be modified or amended with approval from the Fund.
2. The expense example table that appears under the caption "Fees and Expenses of the Fund – Example" in the "Summary of the Fund" section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following:
    
  1 year 3 years 5 years 10 years
Class A (whether or not shares are redeemed) $709 $993 $1,297 $2,158
Class C (assuming redemption of all shares at the end of the period) $318 $673 $1,154 $2,483
Class C (assuming no redemption of shares) $218 $673 $1,154 $2,483
Class I (whether or not shares are redeemed) $104 $325 $ 563 $1,248
Class R4 (whether or not shares are redeemed) $117 $365 $ 633 $1,398
Class R5 (whether or not shares are redeemed) $109 $340 $ 590 $1,306
Class Y (whether or not shares are redeemed) $121 $378 $ 654 $1,443
Class Z (whether or not shares are redeemed) $117 $365 $ 633 $1,398 
Columbia Acorn International Select  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat4_SupplementTextBlock
Supplement dated June 27, 2016
to the Prospectus, Summary Prospectus and Statement of Additional Information ("SAI") of the following Fund:
Fund Prospectus, Summary Prospectus and SAI Dated
Columbia Acorn Trust  
    Columbia Acorn International SelectSM 5/1/2016
1. The table under the caption "Fees and Expenses of the Fund" in the "Summary of the Fund" section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following:
    
Shareholder Fees (fees paid directly from your investment)
  Class A Class C Classes I, R4,
R5, Y and Z
Maximum sales charge (load) imposed on purchases (as a % of offering price) 5.75% None None
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) 1.00% (a) 1.00% (b) None
    
Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
  Class A Class C Class I Class R4 Class R5 Class Y Class Z
Management fees(c) 0.89% 0.89% 0.89% 0.89% 0.89% 0.89% 0.89%
Distribution and/or service (12b-1) fees 0.25% 1.00% 0.00% 0.00% 0.00% 0.00% 0.00%
Other expenses(d) 0.42% 0.42% 0.30% 0.42% 0.35% 0.30% 0.42%
Total annual Fund operating expenses 1.56% 2.31% 1.19% 1.31% 1.24% 1.19% 1.31%
Less: Fee waivers and/or expense reimbursements(e) (0.16%) (0.16%) (0.17%) (0.16%) (0.17%) (0.17%) (0.16%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements 1.40% 2.15% 1.02% 1.15% 1.07% 1.02% 1.15%
(a) 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.
(b) This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.
(c) Management fees have been restated to reflect current fees based on current asset levels and the contractual agreement of Columbia Wanger Asset Management, LLC (the Investment Manager), effective July 1, 2016, to permanently reduce the investment advisory fee paid by the Fund by 0.05% at all net asset levels.
(d) 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 and changes in the method of allocating transfer agent expenses among Class A, Class C, Class R4 and Class Z shares of the Fund.
(e) Effective July 1, 2016, the Investment Manager has contractually agreed to indefinitely waive fees and reimburse certain expenses of the Fund 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, 2.15% for Class C shares, 1.02% for Class I shares, 1.15% for Class R4 shares, 1.07% for Class R5 shares, 1.02% for Class Y shares and 1.15% for Class Z shares. This arrangement may only be modified or amended with approval from the Fund.
2. The expense example table that appears under the caption "Fees and Expenses of the Fund – Example" in the "Summary of the Fund" section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following:
    
  1 year 3 years 5 years 10 years
Class A (whether or not shares are redeemed) $709 $993 $1,297 $2,158
Class C (assuming redemption of all shares at the end of the period) $318 $673 $1,154 $2,483
Class C (assuming no redemption of shares) $218 $673 $1,154 $2,483
Class I (whether or not shares are redeemed) $104 $325 $ 563 $1,248
Class R4 (whether or not shares are redeemed) $117 $365 $ 633 $1,398
Class R5 (whether or not shares are redeemed) $109 $340 $ 590 $1,306
Class Y (whether or not shares are redeemed) $121 $378 $ 654 $1,443
Class Z (whether or not shares are redeemed) $117 $365 $ 633 $1,398 
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)
Expenses Restated to Reflect Current [Text] rr_ExpensesRestatedToReflectCurrent Management fees have been restated to reflect current fees based on current asset levels and the contractual agreement of Columbia Wanger Asset Management, LLC (the Investment Manager), effective July 1, 2016, to permanently reduce the investment advisory fee paid by the Fund by 0.05% at all net 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 and changes in the method of allocating transfer agent expenses among Class A, Class C, Class R4 and Class Z shares of the Fund.
Columbia Acorn International Select | 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 0.42% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.56%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.16%) [4]
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 993
5 years rr_ExpenseExampleYear05 1,297
10 years rr_ExpenseExampleYear10 2,158
1 year rr_ExpenseExampleNoRedemptionYear01 709
3 years rr_ExpenseExampleNoRedemptionYear03 993
5 years rr_ExpenseExampleNoRedemptionYear05 1,297
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,158
Columbia Acorn International Select | Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a % of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) rr_MaximumDeferredSalesChargeOverOther 1.00% [5]
Management fees rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.42% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 2.31%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.16%) [4]
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 673
5 years rr_ExpenseExampleYear05 1,154
10 years rr_ExpenseExampleYear10 2,483
1 year rr_ExpenseExampleNoRedemptionYear01 218
3 years rr_ExpenseExampleNoRedemptionYear03 673
5 years rr_ExpenseExampleNoRedemptionYear05 1,154
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,483
Columbia Acorn International Select | 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 0.30% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.19%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.17%) [4]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.02%
1 year rr_ExpenseExampleYear01 $ 104
3 years rr_ExpenseExampleYear03 325
5 years rr_ExpenseExampleYear05 563
10 years rr_ExpenseExampleYear10 1,248
1 year rr_ExpenseExampleNoRedemptionYear01 104
3 years rr_ExpenseExampleNoRedemptionYear03 325
5 years rr_ExpenseExampleNoRedemptionYear05 563
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,248
Columbia Acorn International Select | 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 0.42% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.31%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.16%) [4]
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 365
5 years rr_ExpenseExampleYear05 633
10 years rr_ExpenseExampleYear10 1,398
1 year rr_ExpenseExampleNoRedemptionYear01 117
3 years rr_ExpenseExampleNoRedemptionYear03 365
5 years rr_ExpenseExampleNoRedemptionYear05 633
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,398
Columbia Acorn International Select | 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 0.35% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.24%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.17%) [4]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.07%
1 year rr_ExpenseExampleYear01 $ 109
3 years rr_ExpenseExampleYear03 340
5 years rr_ExpenseExampleYear05 590
10 years rr_ExpenseExampleYear10 1,306
1 year rr_ExpenseExampleNoRedemptionYear01 109
3 years rr_ExpenseExampleNoRedemptionYear03 340
5 years rr_ExpenseExampleNoRedemptionYear05 590
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,306
Columbia Acorn International Select | 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 0.30% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.19%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.17%) [4]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.02%
1 year rr_ExpenseExampleYear01 $ 121
3 years rr_ExpenseExampleYear03 378
5 years rr_ExpenseExampleYear05 654
10 years rr_ExpenseExampleYear10 1,443
1 year rr_ExpenseExampleNoRedemptionYear01 121
3 years rr_ExpenseExampleNoRedemptionYear03 378
5 years rr_ExpenseExampleNoRedemptionYear05 654
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,443
Columbia Acorn International Select | 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 0.42% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.31%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.16%) [4]
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 365
5 years rr_ExpenseExampleYear05 633
10 years rr_ExpenseExampleYear10 1,398
1 year rr_ExpenseExampleNoRedemptionYear01 117
3 years rr_ExpenseExampleNoRedemptionYear03 365
5 years rr_ExpenseExampleNoRedemptionYear05 633
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,398
[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 and the contractual agreement of Columbia Wanger Asset Management, LLC (the Investment Manager), effective July 1, 2016, to permanently reduce the investment advisory fee paid by the Fund by 0.05% at all net 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 and changes in the method of allocating transfer agent expenses among Class A, Class C, Class R4 and Class Z shares of the Fund.
[4] Effective July 1, 2016, the Investment Manager has contractually agreed to indefinitely waive fees and reimburse certain expenses of the Fund 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, 2.15% for Class C shares, 1.02% for Class I shares, 1.15% for Class R4 shares, 1.07% for Class R5 shares, 1.02% for Class Y shares and 1.15% for Class Z shares. This arrangement may only be modified or amended with approval from the Fund.
[5] This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.