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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] cat_SupplementTextBlock
Supplement dated March 10, 2017
to the Prospectuses and Summary Prospectuses (each as supplemented) of each of the following Funds (each a
Fund and together the Funds):
Fund Prospectuses and Summary Prospectuses Dated
Columbia Acorn Trust  
 Columbia Acorn Fund 5/1/2016
 Columbia Acorn International 5/1/2016
 Columbia Acorn USA 5/1/2016
 Columbia Acorn International Select 5/1/2016
 Columbia Acorn Select 5/1/2016
 Columbia Thermostat Fund 5/1/2016
 Columbia Acorn Emerging Markets Fund 5/1/2016
 Columbia Acorn European Fund 5/1/2016
Effective April 10, 2017, the information beneath the caption "Fees and Expenses of the Fund" in the Summary Prospectus and in the section entitled "Summary of the Fund" in the Prospectus is hereby revised to insert the following information:
An investor transacting in a class of Fund shares without any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution may be required to pay a commission to the broker/financial intermediary for effecting such transactions. Such commissions are not reflected in the tables or the example below.

The rest of the section remains unchanged.
Columbia Acorn Fund  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat_SupplementTextBlock
Supplement dated March 10, 2017
to the Prospectuses and Summary Prospectuses (each as supplemented) of each of the following Funds (each a
Fund and together the Funds):
Fund Prospectuses and Summary Prospectuses Dated
Columbia Acorn Trust  
 Columbia Acorn Fund 5/1/2016
Effective April 10, 2017, the information beneath the caption "Fees and Expenses of the Fund" in the Summary Prospectus and in the section entitled "Summary of the Fund" in the Prospectus is hereby revised to insert the following information:
An investor transacting in a class of Fund shares without any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution may be required to pay a commission to the broker/financial intermediary for effecting such transactions. Such commissions are not reflected in the tables or the example below.

The rest of the section remains unchanged.
Columbia Acorn International  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat_SupplementTextBlock
Supplement dated March 10, 2017
to the Prospectuses and Summary Prospectuses (each as supplemented) of each of the following Funds (each a
Fund and together the Funds):
Fund Prospectuses and Summary Prospectuses Dated
Columbia Acorn Trust  
 Columbia Acorn International 5/1/2016
Effective April 10, 2017, the information beneath the caption "Fees and Expenses of the Fund" in the Summary Prospectus and in the section entitled "Summary of the Fund" in the Prospectus is hereby revised to insert the following information:
An investor transacting in a class of Fund shares without any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution may be required to pay a commission to the broker/financial intermediary for effecting such transactions. Such commissions are not reflected in the tables or the example below.

The rest of the section remains unchanged.
Columbia Acorn USA  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat_SupplementTextBlock
Supplement dated March 10, 2017
to the Prospectuses and Summary Prospectuses (each as supplemented) of each of the following Funds (each a
Fund and together the Funds):
Fund Prospectuses and Summary Prospectuses Dated
Columbia Acorn Trust  
 Columbia Acorn USA 5/1/2016
Effective April 10, 2017, the information beneath the caption "Fees and Expenses of the Fund" in the Summary Prospectus and in the section entitled "Summary of the Fund" in the Prospectus is hereby revised to insert the following information:
An investor transacting in a class of Fund shares without any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution may be required to pay a commission to the broker/financial intermediary for effecting such transactions. Such commissions are not reflected in the tables or the example below.

The rest of the section remains unchanged.
Columbia Acorn International Select  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat_SupplementTextBlock
Supplement dated March 10, 2017
to the Prospectuses and Summary Prospectuses (each as supplemented) of each of the following Funds (each a
Fund and together the Funds):
Fund Prospectuses and Summary Prospectuses Dated
Columbia Acorn Trust  
 Columbia Acorn International Select 5/1/2016
Effective April 10, 2017, the information beneath the caption "Fees and Expenses of the Fund" in the Summary Prospectus and in the section entitled "Summary of the Fund" in the Prospectus is hereby revised to insert the following information:
An investor transacting in a class of Fund shares without any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution may be required to pay a commission to the broker/financial intermediary for effecting such transactions. Such commissions are not reflected in the tables or the example below.

The rest of the section remains unchanged.
Columbia Acorn Select  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat_SupplementTextBlock
Supplement dated March 10, 2017
to the Prospectuses and Summary Prospectuses (each as supplemented) of each of the following Funds (each a
Fund and together the Funds):
Fund Prospectuses and Summary Prospectuses Dated
Columbia Acorn Trust  
 Columbia Acorn Select 5/1/2016
Effective April 10, 2017, the information beneath the caption "Fees and Expenses of the Fund" in the Summary Prospectus and in the section entitled "Summary of the Fund" in the Prospectus is hereby revised to insert the following information:
An investor transacting in a class of Fund shares without any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution may be required to pay a commission to the broker/financial intermediary for effecting such transactions. Such commissions are not reflected in the tables or the example below.

The rest of the section remains unchanged.
Columbia Thermostat Fund  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat_SupplementTextBlock
Supplement dated March 10, 2017
to the Prospectuses and Summary Prospectuses (each as supplemented) of each of the following Funds (each a
Fund and together the Funds):
Fund Prospectuses and Summary Prospectuses Dated
Columbia Acorn Trust  
 Columbia Thermostat Fund 5/1/2016
Effective April 10, 2017, the information beneath the caption "Fees and Expenses of the Fund" in the Summary Prospectus and in the section entitled "Summary of the Fund" in the Prospectus is hereby revised to insert the following information:
An investor transacting in a class of Fund shares without any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution may be required to pay a commission to the broker/financial intermediary for effecting such transactions. Such commissions are not reflected in the tables or the example below.

The rest of the section remains unchanged.
Columbia Acorn Emerging Markets Fund  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat_SupplementTextBlock
Supplement dated March 10, 2017
to the Prospectuses and Summary Prospectuses (each as supplemented) of each of the following Funds (each a
Fund and together the Funds):
Fund Prospectuses and Summary Prospectuses Dated
Columbia Acorn Trust  
 Columbia Acorn Emerging Markets Fund 5/1/2016
Effective April 10, 2017, the information beneath the caption "Fees and Expenses of the Fund" in the Summary Prospectus and in the section entitled "Summary of the Fund" in the Prospectus is hereby revised to insert the following information:
An investor transacting in a class of Fund shares without any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution may be required to pay a commission to the broker/financial intermediary for effecting such transactions. Such commissions are not reflected in the tables or the example below.

The rest of the section remains unchanged.
Columbia Acorn European Fund  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] cat_SupplementTextBlock
Supplement dated March 10, 2017
to the Prospectuses and Summary Prospectuses (each as supplemented) of each of the following Funds (each a
Fund and together the Funds):
Fund Prospectuses and Summary Prospectuses Dated
Columbia Acorn Trust  
 Columbia Acorn European Fund 5/1/2016
Effective April 10, 2017, the information beneath the caption "Fees and Expenses of the Fund" in the Summary Prospectus and in the section entitled "Summary of the Fund" in the Prospectus is hereby revised to insert the following information:
An investor transacting in a class of Fund shares without any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution may be required to pay a commission to the broker/financial intermediary for effecting such transactions. Such commissions are not reflected in the tables or the example below.

The rest of the section remains unchanged.