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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] cat5_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 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and Expenses of the Fund” in the “Summary of the Fund” section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following: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 0.85% 0.85% 0.85% 0.85% 0.85% 0.85% 0.85%
Distribution and/or service (12b-1) fees 0.25% 1.00% 0.00% 0.00% 0.00% 0.00% 0.00%
Other expenses(c) 0.23% 0.23% 0.12% 0.23% 0.17% 0.12% 0.23%
Total annual Fund operating expenses 1.33% 2.08% 0.97% 1.08% 1.02% 0.97% 1.08%
Less: Fee waivers and/or expense reimbursements(d) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements 1.13% 1.88% 0.77% 0.88% 0.82% 0.77% 0.88%
(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 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.
(d) Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive 0.20% of the advisory fee otherwise payable to it by the Fund 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) $684 $954 $1,244 $2,068
Class C (assuming redemption of all shares at the end of the period) $291 $633 $1,100 $2,395
Class C (assuming no redemption of shares) $191 $633 $1,100 $2,395
Class I (whether or not shares are redeemed) $ 79 $289 $ 517 $1,171
Class R4 (whether or not shares are redeemed) $ 90 $324 $ 576 $1,299
Class R5 (whether or not shares are redeemed) $ 84 $305 $ 544 $1,230
Class Y (whether or not shares are redeemed) $ 79 $289 $ 517 $1,171
Class Z (whether or not shares are redeemed) $ 90 $324 $ 576 $1,299
Columbia Acorn Select  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat5_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 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 0.85% 0.85% 0.85% 0.85% 0.85% 0.85% 0.85%
Distribution and/or service (12b-1) fees 0.25% 1.00% 0.00% 0.00% 0.00% 0.00% 0.00%
Other expenses(c) 0.23% 0.23% 0.12% 0.23% 0.17% 0.12% 0.23%
Total annual Fund operating expenses 1.33% 2.08% 0.97% 1.08% 1.02% 0.97% 1.08%
Less: Fee waivers and/or expense reimbursements(d) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements 1.13% 1.88% 0.77% 0.88% 0.82% 0.77% 0.88%
(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 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.
(d) Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive 0.20% of the advisory fee otherwise payable to it by the Fund 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) $684 $954 $1,244 $2,068
Class C (assuming redemption of all shares at the end of the period) $291 $633 $1,100 $2,395
Class C (assuming no redemption of shares) $191 $633 $1,100 $2,395
Class I (whether or not shares are redeemed) $ 79 $289 $ 517 $1,171
Class R4 (whether or not shares are redeemed) $ 90 $324 $ 576 $1,299
Class R5 (whether or not shares are redeemed) $ 84 $305 $ 544 $1,230
Class Y (whether or not shares are redeemed) $ 79 $289 $ 517 $1,171
Class Z (whether or not shares are redeemed) $ 90 $324 $ 576 $1,299
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.
Columbia Acorn 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 0.85%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.23% [2]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.33%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.20%) [3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.13%
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 $ 684
3 years rr_ExpenseExampleYear03 954
5 years rr_ExpenseExampleYear05 1,244
10 years rr_ExpenseExampleYear10 2,068
1 year rr_ExpenseExampleNoRedemptionYear01 684
3 years rr_ExpenseExampleNoRedemptionYear03 954
5 years rr_ExpenseExampleNoRedemptionYear05 1,244
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,068
Columbia Acorn 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% [4]
Management fees rr_ManagementFeesOverAssets 0.85%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.23% [2]
Total annual Fund operating expenses rr_ExpensesOverAssets 2.08%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.20%) [3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 1.88%
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 $ 291
3 years rr_ExpenseExampleYear03 633
5 years rr_ExpenseExampleYear05 1,100
10 years rr_ExpenseExampleYear10 2,395
1 year rr_ExpenseExampleNoRedemptionYear01 191
3 years rr_ExpenseExampleNoRedemptionYear03 633
5 years rr_ExpenseExampleNoRedemptionYear05 1,100
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,395
Columbia Acorn 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 0.85%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.12% [2]
Total annual Fund operating expenses rr_ExpensesOverAssets 0.97%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.20%) [3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 0.77%
1 year rr_ExpenseExampleYear01 $ 79
3 years rr_ExpenseExampleYear03 289
5 years rr_ExpenseExampleYear05 517
10 years rr_ExpenseExampleYear10 1,171
1 year rr_ExpenseExampleNoRedemptionYear01 79
3 years rr_ExpenseExampleNoRedemptionYear03 289
5 years rr_ExpenseExampleNoRedemptionYear05 517
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,171
Columbia Acorn 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 0.85%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.23% [2]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.08%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.20%) [3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 0.88%
1 year rr_ExpenseExampleYear01 $ 90
3 years rr_ExpenseExampleYear03 324
5 years rr_ExpenseExampleYear05 576
10 years rr_ExpenseExampleYear10 1,299
1 year rr_ExpenseExampleNoRedemptionYear01 90
3 years rr_ExpenseExampleNoRedemptionYear03 324
5 years rr_ExpenseExampleNoRedemptionYear05 576
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,299
Columbia Acorn 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 0.85%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.17% [2]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.02%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.20%) [3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 0.82%
1 year rr_ExpenseExampleYear01 $ 84
3 years rr_ExpenseExampleYear03 305
5 years rr_ExpenseExampleYear05 544
10 years rr_ExpenseExampleYear10 1,230
1 year rr_ExpenseExampleNoRedemptionYear01 84
3 years rr_ExpenseExampleNoRedemptionYear03 305
5 years rr_ExpenseExampleNoRedemptionYear05 544
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,230
Columbia Acorn 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 0.85%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.12% [2]
Total annual Fund operating expenses rr_ExpensesOverAssets 0.97%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.20%) [3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 0.77%
1 year rr_ExpenseExampleYear01 $ 79
3 years rr_ExpenseExampleYear03 289
5 years rr_ExpenseExampleYear05 517
10 years rr_ExpenseExampleYear10 1,171
1 year rr_ExpenseExampleNoRedemptionYear01 79
3 years rr_ExpenseExampleNoRedemptionYear03 289
5 years rr_ExpenseExampleNoRedemptionYear05 517
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,171
Columbia Acorn 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 0.85%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.23% [2]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.08%
Less: Fee waivers and/or expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.20%) [3]
Total annual Fund operating expenses after fee waivers and/or expense reimbursements rr_NetExpensesOverAssets 0.88%
1 year rr_ExpenseExampleYear01 $ 90
3 years rr_ExpenseExampleYear03 324
5 years rr_ExpenseExampleYear05 576
10 years rr_ExpenseExampleYear10 1,299
1 year rr_ExpenseExampleNoRedemptionYear01 90
3 years rr_ExpenseExampleNoRedemptionYear03 324
5 years rr_ExpenseExampleNoRedemptionYear05 576
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,299
[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
[2] Other expenses have been restated 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.
[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive 0.20% of the advisory fee otherwise payable to it by the Fund through April 30, 2017. This arrangement may only be modified or amended with approval from the Fund and the Investment Manager.
[4] This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.