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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] cat1_SupplementTextBlock
Supplement dated June 27, 2016
to the Prospectus and Summary Prospectus of the following Fund:
Fund Prospectus and Summary Prospectus Dated
Columbia Acorn Trust  
   Columbia Acorn European FundSM 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and Expenses of the Fund” in the “Summary of the Fund” section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following: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 1.19% 1.19% 1.19% 1.19% 1.19% 1.19% 1.19%
Distribution and/or service (12b-1) fees 0.25% 1.00% 0.00% 0.00% 0.00% 0.00% 0.00%
Other expenses(c)(d) 0.61% 0.61% 0.50% 0.61% 0.55% 0.50% 0.61%
Acquired fund fees and expenses 0.01% 0.01% 0.01% 0.01% 0.01% 0.01% 0.01%
Total annual Fund operating expenses(e) 2.06% 2.81% 1.70% 1.81% 1.75% 1.70% 1.81%
Fee waivers and/or expense reimbursements(f) (0.30%) (0.30%) (0.27%) (0.30%) (0.27%) (0.27%) (0.30%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements 1.76% 2.51% 1.43% 1.51% 1.48% 1.43% 1.51%
(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) Other expenses for Class Y shares are based on estimated amounts for the Fund's current fiscal year.
(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 method of allocating transfer agent expenses among Class A, Class C, Class R4 and Class Z shares of the Fund.
(e) "Total annual Fund operating expenses" include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than "Total Net Expenses" shown in the Financial Highlights section of this prospectus because "Total Net Expenses" do not include acquired fund fees and expenses.
(f) Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to 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 1.75% for Class A shares, 2.50% for Class C shares, 1.42% for Class I shares, 1.50% for Class R4 shares, 1.47% for Class R5 shares, 1.42% for Class Y shares and 1.50% for Class Z shares, through April 30, 2017.This arrangement may only be modified or amended with approval from the Fund and the Investment Manager.
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) $744 $1,156 $1,594 $2,805
Class C (assuming redemption of all shares at the end of the period) $354 $ 843 $1,458 $3,116
Class C (assuming no redemption of shares) $254 $ 843 $1,458 $3,116
Class I (whether or not shares are redeemed) $146 $ 509 $ 898 $1,986
Class R4 (whether or not shares are redeemed) $154 $ 540 $ 952 $2,102
Class R5 (whether or not shares are redeemed) $151 $ 525 $ 924 $2,040
Class Y (whether or not shares are redeemed) $146 $ 509 $ 898 $1,986
Class Z (whether or not shares are redeemed) $154 $ 540 $ 952 $2,102 
Columbia Acorn European Fund  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat1_SupplementTextBlock
Supplement dated June 27, 2016
to the Prospectus and Summary Prospectus of the following Fund:
Fund Prospectus and Summary Prospectus Dated
Columbia Acorn Trust  
   Columbia Acorn European FundSM 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 1.19% 1.19% 1.19% 1.19% 1.19% 1.19% 1.19%
Distribution and/or service (12b-1) fees 0.25% 1.00% 0.00% 0.00% 0.00% 0.00% 0.00%
Other expenses(c)(d) 0.61% 0.61% 0.50% 0.61% 0.55% 0.50% 0.61%
Acquired fund fees and expenses 0.01% 0.01% 0.01% 0.01% 0.01% 0.01% 0.01%
Total annual Fund operating expenses(e) 2.06% 2.81% 1.70% 1.81% 1.75% 1.70% 1.81%
Fee waivers and/or expense reimbursements(f) (0.30%) (0.30%) (0.27%) (0.30%) (0.27%) (0.27%) (0.30%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements 1.76% 2.51% 1.43% 1.51% 1.48% 1.43% 1.51%
(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) Other expenses for Class Y shares are based on estimated amounts for the Fund's current fiscal year.
(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 method of allocating transfer agent expenses among Class A, Class C, Class R4 and Class Z shares of the Fund.
(e) "Total annual Fund operating expenses" include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than "Total Net Expenses" shown in the Financial Highlights section of this prospectus because "Total Net Expenses" do not include acquired fund fees and expenses.
(f) Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to 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 1.75% for Class A shares, 2.50% for Class C shares, 1.42% for Class I shares, 1.50% for Class R4 shares, 1.47% for Class R5 shares, 1.42% for Class Y shares and 1.50% for Class Z shares, through April 30, 2017.This arrangement may only be modified or amended with approval from the Fund and the Investment Manager.
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) $744 $1,156 $1,594 $2,805
Class C (assuming redemption of all shares at the end of the period) $354 $ 843 $1,458 $3,116
Class C (assuming no redemption of shares) $254 $ 843 $1,458 $3,116
Class I (whether or not shares are redeemed) $146 $ 509 $ 898 $1,986
Class R4 (whether or not shares are redeemed) $154 $ 540 $ 952 $2,102
Class R5 (whether or not shares are redeemed) $151 $ 525 $ 924 $2,040
Class Y (whether or not shares are redeemed) $146 $ 509 $ 898 $1,986
Class Z (whether or not shares are redeemed) $154 $ 540 $ 952 $2,102 
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, 2017
Expenses Restated to Reflect Current [Text] rr_ExpensesRestatedToReflectCurrent Other expenses have been restated and are based on estimated amounts for the Fund's current fiscal year, taking into consideration changes in the method of allocating transfer agent expenses among Class A, Class C, Class R4 and Class Z shares of the Fund.
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees "Total annual Fund operating expenses" include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than "Total Net Expenses" shown in the Financial Highlights section of this prospectus because "Total Net Expenses" do not include acquired fund fees and expenses.
Columbia Acorn European Fund | Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a % of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) rr_MaximumDeferredSalesChargeOverOther 1.00% [1]
Management fees rr_ManagementFeesOverAssets 1.19%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.61% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 2.06% [4]
Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.30%) [5]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.76%
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 $ 744
3 years rr_ExpenseExampleYear03 1,156
5 years rr_ExpenseExampleYear05 1,594
10 years rr_ExpenseExampleYear10 2,805
1 year rr_ExpenseExampleNoRedemptionYear01 744
3 years rr_ExpenseExampleNoRedemptionYear03 1,156
5 years rr_ExpenseExampleNoRedemptionYear05 1,594
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,805
Columbia Acorn European Fund | Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a % of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) rr_MaximumDeferredSalesChargeOverOther 1.00% [6]
Management fees rr_ManagementFeesOverAssets 1.19%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.61% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 2.81% [4]
Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.30%) [5]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 2.51%
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 $ 354
3 years rr_ExpenseExampleYear03 843
5 years rr_ExpenseExampleYear05 1,458
10 years rr_ExpenseExampleYear10 3,116
1 year rr_ExpenseExampleNoRedemptionYear01 254
3 years rr_ExpenseExampleNoRedemptionYear03 843
5 years rr_ExpenseExampleNoRedemptionYear05 1,458
10 years rr_ExpenseExampleNoRedemptionYear10 $ 3,116
Columbia Acorn European Fund | 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 1.19%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.50% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.70% [4]
Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.27%) [5]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.43%
1 year rr_ExpenseExampleYear01 $ 146
3 years rr_ExpenseExampleYear03 509
5 years rr_ExpenseExampleYear05 898
10 years rr_ExpenseExampleYear10 1,986
1 year rr_ExpenseExampleNoRedemptionYear01 146
3 years rr_ExpenseExampleNoRedemptionYear03 509
5 years rr_ExpenseExampleNoRedemptionYear05 898
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,986
Columbia Acorn European Fund | 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 1.19%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.61% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.81% [4]
Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.30%) [5]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.51%
1 year rr_ExpenseExampleYear01 $ 154
3 years rr_ExpenseExampleYear03 540
5 years rr_ExpenseExampleYear05 952
10 years rr_ExpenseExampleYear10 2,102
1 year rr_ExpenseExampleNoRedemptionYear01 154
3 years rr_ExpenseExampleNoRedemptionYear03 540
5 years rr_ExpenseExampleNoRedemptionYear05 952
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,102
Columbia Acorn European Fund | 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 1.19%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.55% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.75% [4]
Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.27%) [5]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.48%
1 year rr_ExpenseExampleYear01 $ 151
3 years rr_ExpenseExampleYear03 525
5 years rr_ExpenseExampleYear05 924
10 years rr_ExpenseExampleYear10 2,040
1 year rr_ExpenseExampleNoRedemptionYear01 151
3 years rr_ExpenseExampleNoRedemptionYear03 525
5 years rr_ExpenseExampleNoRedemptionYear05 924
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,040
Columbia Acorn European Fund | 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 1.19%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.50% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.70% [4]
Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.27%) [5]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.43%
1 year rr_ExpenseExampleYear01 $ 146
3 years rr_ExpenseExampleYear03 509
5 years rr_ExpenseExampleYear05 898
10 years rr_ExpenseExampleYear10 1,986
1 year rr_ExpenseExampleNoRedemptionYear01 146
3 years rr_ExpenseExampleNoRedemptionYear03 509
5 years rr_ExpenseExampleNoRedemptionYear05 898
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,986
Columbia Acorn European Fund | 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 1.19%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.61% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.81% [4]
Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.30%) [5]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.51%
1 year rr_ExpenseExampleYear01 $ 154
3 years rr_ExpenseExampleYear03 540
5 years rr_ExpenseExampleYear05 952
10 years rr_ExpenseExampleYear10 2,102
1 year rr_ExpenseExampleNoRedemptionYear01 154
3 years rr_ExpenseExampleNoRedemptionYear03 540
5 years rr_ExpenseExampleNoRedemptionYear05 952
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,102
[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 for Class Y shares are based on estimated amounts for the Fund's current fiscal year.
[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 method of allocating transfer agent expenses among Class A, Class C, Class R4 and Class Z shares of the Fund.
[4] "Total annual Fund operating expenses" include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than "Total Net Expenses" shown in the Financial Highlights section of this prospectus because "Total Net Expenses" do not include acquired fund fees and expenses.
[5] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to 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 1.75% for Class A shares, 2.50% for Class C shares, 1.42% for Class I shares, 1.50% for Class R4 shares, 1.47% for Class R5 shares, 1.42% for Class Y shares and 1.50% for Class Z shares, through April 30, 2017.This arrangement may only be modified or amended with approval from the Fund and the Investment Manager.
[6] This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.