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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] cat6_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 USA® 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and Expenses of the Fund” in the “Summary of the Fund” section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following: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) 0.29% 0.29% 0.14% 0.29% 0.19% 0.14% 0.29%
Total annual Fund operating expenses 1.43% 2.18% 1.03% 1.18% 1.08% 1.03% 1.18%
(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.
(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.
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of the Fund – Example” in the “Summary of the Fund” section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following: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) $712 $1,001 $1,312 $2,190
Class C (assuming redemption of all shares at the end of the period) $321 $ 682 $1,169 $2,513
Class C (assuming no redemption of shares) $221 $ 682 $1,169 $2,513
Class I (whether or not shares are redeemed) $105 $ 328 $ 569 $1,259
Class R4 (whether or not shares are redeemed) $120 $ 375 $ 649 $1,432
Class R5 (whether or not shares are redeemed) $110 $ 343 $ 595 $1,317
Class Y (whether or not shares are redeemed) $105 $ 328 $ 569 $1,259
Class Z (whether or not shares are redeemed) $120 $ 375 $ 649 $1,432
Columbia Acorn USA  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat6_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 USA® 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) 0.29% 0.29% 0.14% 0.29% 0.19% 0.14% 0.29%
Total annual Fund operating expenses 1.43% 2.18% 1.03% 1.18% 1.08% 1.03% 1.18%
(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.
(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.
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) $712 $1,001 $1,312 $2,190
Class C (assuming redemption of all shares at the end of the period) $321 $ 682 $1,169 $2,513
Class C (assuming no redemption of shares) $221 $ 682 $1,169 $2,513
Class I (whether or not shares are redeemed) $105 $ 328 $ 569 $1,259
Class R4 (whether or not shares are redeemed) $120 $ 375 $ 649 $1,432
Class R5 (whether or not shares are redeemed) $110 $ 343 $ 595 $1,317
Class Y (whether or not shares are redeemed) $105 $ 328 $ 569 $1,259
Class Z (whether or not shares are redeemed) $120 $ 375 $ 649 $1,432
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.

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 USA | Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a % of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) rr_MaximumDeferredSalesChargeOverOther 1.00% [1]
Management fees rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.29% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.43%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
1 year rr_ExpenseExampleYear01 $ 712
3 years rr_ExpenseExampleYear03 1,001
5 years rr_ExpenseExampleYear05 1,312
10 years rr_ExpenseExampleYear10 2,190
1 year rr_ExpenseExampleNoRedemptionYear01 712
3 years rr_ExpenseExampleNoRedemptionYear03 1,001
5 years rr_ExpenseExampleNoRedemptionYear05 1,312
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,190
Columbia Acorn USA | Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a % of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) rr_MaximumDeferredSalesChargeOverOther 1.00% [4]
Management fees rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.29% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 2.18%
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 $ 321
3 years rr_ExpenseExampleYear03 682
5 years rr_ExpenseExampleYear05 1,169
10 years rr_ExpenseExampleYear10 2,513
1 year rr_ExpenseExampleNoRedemptionYear01 221
3 years rr_ExpenseExampleNoRedemptionYear03 682
5 years rr_ExpenseExampleNoRedemptionYear05 1,169
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,513
Columbia Acorn USA | Class I  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a % of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) rr_MaximumDeferredSalesChargeOverOther none
Management fees rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.14% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.03%
1 year rr_ExpenseExampleYear01 $ 105
3 years rr_ExpenseExampleYear03 328
5 years rr_ExpenseExampleYear05 569
10 years rr_ExpenseExampleYear10 1,259
1 year rr_ExpenseExampleNoRedemptionYear01 105
3 years rr_ExpenseExampleNoRedemptionYear03 328
5 years rr_ExpenseExampleNoRedemptionYear05 569
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,259
Columbia Acorn USA | Class R4  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a % of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) rr_MaximumDeferredSalesChargeOverOther none
Management fees rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.29% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.18%
1 year rr_ExpenseExampleYear01 $ 120
3 years rr_ExpenseExampleYear03 375
5 years rr_ExpenseExampleYear05 649
10 years rr_ExpenseExampleYear10 1,432
1 year rr_ExpenseExampleNoRedemptionYear01 120
3 years rr_ExpenseExampleNoRedemptionYear03 375
5 years rr_ExpenseExampleNoRedemptionYear05 649
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,432
Columbia Acorn USA | Class R5  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a % of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) rr_MaximumDeferredSalesChargeOverOther none
Management fees rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.19% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.08%
1 year rr_ExpenseExampleYear01 $ 110
3 years rr_ExpenseExampleYear03 343
5 years rr_ExpenseExampleYear05 595
10 years rr_ExpenseExampleYear10 1,317
1 year rr_ExpenseExampleNoRedemptionYear01 110
3 years rr_ExpenseExampleNoRedemptionYear03 343
5 years rr_ExpenseExampleNoRedemptionYear05 595
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,317
Columbia Acorn USA | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a % of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) rr_MaximumDeferredSalesChargeOverOther none
Management fees rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.14% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.03%
1 year rr_ExpenseExampleYear01 $ 105
3 years rr_ExpenseExampleYear03 328
5 years rr_ExpenseExampleYear05 569
10 years rr_ExpenseExampleYear10 1,259
1 year rr_ExpenseExampleNoRedemptionYear01 105
3 years rr_ExpenseExampleNoRedemptionYear03 328
5 years rr_ExpenseExampleNoRedemptionYear05 569
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,259
Columbia Acorn USA | Class Z  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a % of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value) rr_MaximumDeferredSalesChargeOverOther none
Management fees rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.29% [3]
Total annual Fund operating expenses rr_ExpensesOverAssets 1.18%
1 year rr_ExpenseExampleYear01 $ 120
3 years rr_ExpenseExampleYear03 375
5 years rr_ExpenseExampleYear05 649
10 years rr_ExpenseExampleYear10 1,432
1 year rr_ExpenseExampleNoRedemptionYear01 120
3 years rr_ExpenseExampleNoRedemptionYear03 375
5 years rr_ExpenseExampleNoRedemptionYear05 649
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,432
[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
[2] Management fees have been restated to reflect current fees based on current asset levels.
[3] Other expenses have been restated and are based on estimated amounts for the Fund's current fiscal year, taking into consideration changes in the Fund's net assets 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] This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.