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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName COLUMBIA ACORN TRUST
Prospectus Date rr_ProspectusDate May 01, 2016
Supplement [Text Block] cat3_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 International® 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and Expenses of the Fund” in the “Summary of the Fund” section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following: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 B 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 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) 5.00% (b) 1.00% (c) None
    
Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
  Class A Class B Class C Class I Class R Class R4 Class R5 Class Y Class Z
Management fees 0.76% 0.76% 0.76% 0.76% 0.76% 0.76% 0.76% 0.76% 0.76%
Distribution and/or service (12b-1) fees 0.25% 0.75% 1.00% 0.00% 0.50% 0.00% 0.00% 0.00% 0.00%
Other expenses(d)(e) 0.22% 0.11% 0.22% 0.11% 0.22% 0.22% 0.16% 0.11% 0.22%
Acquired fund fees and expenses 0.01% 0.01% 0.01% 0.01% 0.01% 0.01% 0.01% 0.01% 0.01%
Total annual Fund operating expenses(f) 1.24% 1.63% 1.99% 0.88% 1.49% 0.99% 0.93% 0.88% 0.99%
(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 decreases over time.
(c) This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.
(d) Other expenses have been restated to reflect the agreement of the Fund’s transfer agent to contractually waive the transfer agency fees paid by Class B shares of the Fund through April 30, 2017. This fee waiver may only be modified or amended with approval from the Fund’s Board and the Fund’s transfer agent.
(e) 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 B, Class C, Class R, Class R4 and Class Z shares of the Fund.
(f) “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.
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) $694 $946 $1,217 $1,989
Class B (assuming redemption of all shares at the end of the period) $666 $931 $1,323 $2,238
Class B (assuming no redemption of shares) $166 $631 $1,123 $2,238
Class C (assuming redemption of all shares at the end of the period) $302 $624 $1,073 $2,317
Class C (assuming no redemption of shares) $202 $624 $1,073 $2,317
Class I (whether or not shares are redeemed) $ 90 $281 $ 488 $1,084
Class R (whether or not shares are redeemed) $152 $471 $ 813 $1,779
Class R4 (whether or not shares are redeemed) $101 $315 $ 547 $1,213
Class R5 (whether or not shares are redeemed) $ 95 $296 $ 515 $1,143
Class Y (whether or not shares are redeemed) $ 90 $281 $ 488 $1,084
Class Z (whether or not shares are redeemed) $101 $315 $ 547 $1,213
Columbia Acorn International  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat3_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 International® 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 B 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 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) 5.00% (b) 1.00% (c) None
    
Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
  Class A Class B Class C Class I Class R Class R4 Class R5 Class Y Class Z
Management fees 0.76% 0.76% 0.76% 0.76% 0.76% 0.76% 0.76% 0.76% 0.76%
Distribution and/or service (12b-1) fees 0.25% 0.75% 1.00% 0.00% 0.50% 0.00% 0.00% 0.00% 0.00%
Other expenses(d)(e) 0.22% 0.11% 0.22% 0.11% 0.22% 0.22% 0.16% 0.11% 0.22%
Acquired fund fees and expenses 0.01% 0.01% 0.01% 0.01% 0.01% 0.01% 0.01% 0.01% 0.01%
Total annual Fund operating expenses(f) 1.24% 1.63% 1.99% 0.88% 1.49% 0.99% 0.93% 0.88% 0.99%
(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 decreases over time.
(c) This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.
(d) Other expenses have been restated to reflect the agreement of the Fund’s transfer agent to contractually waive the transfer agency fees paid by Class B shares of the Fund through April 30, 2017. This fee waiver may only be modified or amended with approval from the Fund’s Board and the Fund’s transfer agent.
(e) 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 B, Class C, Class R, Class R4 and Class Z shares of the Fund.
(f) “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.
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) $694 $946 $1,217 $1,989
Class B (assuming redemption of all shares at the end of the period) $666 $931 $1,323 $2,238
Class B (assuming no redemption of shares) $166 $631 $1,123 $2,238
Class C (assuming redemption of all shares at the end of the period) $302 $624 $1,073 $2,317
Class C (assuming no redemption of shares) $202 $624 $1,073 $2,317
Class I (whether or not shares are redeemed) $ 90 $281 $ 488 $1,084
Class R (whether or not shares are redeemed) $152 $471 $ 813 $1,779
Class R4 (whether or not shares are redeemed) $101 $315 $ 547 $1,213
Class R5 (whether or not shares are redeemed) $ 95 $296 $ 515 $1,143
Class Y (whether or not shares are redeemed) $ 90 $281 $ 488 $1,084
Class Z (whether or not shares are redeemed) $101 $315 $ 547 $1,213
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 to reflect the agreement of the Fund’s transfer agent to contractually waive the transfer agency fees paid by Class B shares of the Fund through April 30, 2017.

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 B, Class C, Class R, 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 International | 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 0.76%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.22% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.24% [4]
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 $ 694
3 years rr_ExpenseExampleYear03 946
5 years rr_ExpenseExampleYear05 1,217
10 years rr_ExpenseExampleYear10 1,989
1 year rr_ExpenseExampleNoRedemptionYear01 694
3 years rr_ExpenseExampleNoRedemptionYear03 946
5 years rr_ExpenseExampleNoRedemptionYear05 1,217
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,989
Columbia Acorn International | Class B  
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 5.00% [5]
Management fees rr_ManagementFeesOverAssets 0.76%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.75%
Other expenses rr_OtherExpensesOverAssets 0.11% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.63% [4]
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock This charge decreases over time.
1 year rr_ExpenseExampleYear01 $ 666
3 years rr_ExpenseExampleYear03 931
5 years rr_ExpenseExampleYear05 1,323
10 years rr_ExpenseExampleYear10 2,238
1 year rr_ExpenseExampleNoRedemptionYear01 166
3 years rr_ExpenseExampleNoRedemptionYear03 631
5 years rr_ExpenseExampleNoRedemptionYear05 1,123
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,238
Columbia Acorn International | 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 0.76%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.22% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.99% [4]
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 $ 302
3 years rr_ExpenseExampleYear03 624
5 years rr_ExpenseExampleYear05 1,073
10 years rr_ExpenseExampleYear10 2,317
1 year rr_ExpenseExampleNoRedemptionYear01 202
3 years rr_ExpenseExampleNoRedemptionYear03 624
5 years rr_ExpenseExampleNoRedemptionYear05 1,073
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,317
Columbia Acorn International | 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 0.76%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.11% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 0.88% [4]
1 year rr_ExpenseExampleYear01 $ 90
3 years rr_ExpenseExampleYear03 281
5 years rr_ExpenseExampleYear05 488
10 years rr_ExpenseExampleYear10 1,084
1 year rr_ExpenseExampleNoRedemptionYear01 90
3 years rr_ExpenseExampleNoRedemptionYear03 281
5 years rr_ExpenseExampleNoRedemptionYear05 488
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,084
Columbia Acorn International | Class R  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.76%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other expenses rr_OtherExpensesOverAssets 0.22% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 1.49% [4]
1 year rr_ExpenseExampleYear01 $ 152
3 years rr_ExpenseExampleYear03 471
5 years rr_ExpenseExampleYear05 813
10 years rr_ExpenseExampleYear10 1,779
1 year rr_ExpenseExampleNoRedemptionYear01 152
3 years rr_ExpenseExampleNoRedemptionYear03 471
5 years rr_ExpenseExampleNoRedemptionYear05 813
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,779
Columbia Acorn International | 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 0.76%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.22% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 0.99% [4]
1 year rr_ExpenseExampleYear01 $ 101
3 years rr_ExpenseExampleYear03 315
5 years rr_ExpenseExampleYear05 547
10 years rr_ExpenseExampleYear10 1,213
1 year rr_ExpenseExampleNoRedemptionYear01 101
3 years rr_ExpenseExampleNoRedemptionYear03 315
5 years rr_ExpenseExampleNoRedemptionYear05 547
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,213
Columbia Acorn International | 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 0.76%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.16% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 0.93% [4]
1 year rr_ExpenseExampleYear01 $ 95
3 years rr_ExpenseExampleYear03 296
5 years rr_ExpenseExampleYear05 515
10 years rr_ExpenseExampleYear10 1,143
1 year rr_ExpenseExampleNoRedemptionYear01 95
3 years rr_ExpenseExampleNoRedemptionYear03 296
5 years rr_ExpenseExampleNoRedemptionYear05 515
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,143
Columbia Acorn International | 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 0.76%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.11% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 0.88% [4]
1 year rr_ExpenseExampleYear01 $ 90
3 years rr_ExpenseExampleYear03 281
5 years rr_ExpenseExampleYear05 488
10 years rr_ExpenseExampleYear10 1,084
1 year rr_ExpenseExampleNoRedemptionYear01 90
3 years rr_ExpenseExampleNoRedemptionYear03 281
5 years rr_ExpenseExampleNoRedemptionYear05 488
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,084
Columbia Acorn International | 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 0.76%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.22% [2],[3]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total annual Fund operating expenses rr_ExpensesOverAssets 0.99% [4]
1 year rr_ExpenseExampleYear01 $ 101
3 years rr_ExpenseExampleYear03 315
5 years rr_ExpenseExampleYear05 547
10 years rr_ExpenseExampleYear10 1,213
1 year rr_ExpenseExampleNoRedemptionYear01 101
3 years rr_ExpenseExampleNoRedemptionYear03 315
5 years rr_ExpenseExampleNoRedemptionYear05 547
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,213
[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 B, Class C, Class R, Class R4 and Class Z shares of the Fund.
[3] Other expenses have been restated to reflect the agreement of the Fund’s transfer agent to contractually waive the transfer agency fees paid by Class B shares of the Fund through April 30, 2017. This fee waiver may only be modified or amended with approval from the Fund’s Board and the Fund’s transfer agent.
[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] This charge decreases over time.
[6] This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.