Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

COLUMBIA ACORN TRUST

Prospectus Date

rr_ProspectusDate

May 01, 2013

Supplement [Text Block]

cat_SupplementTextblock

COLUMBIA ACORN TRUST

Columbia Acorn Emerging Markets Fund^SM

(the “Fund”)

Supplement dated September 5, 2013

to the Prospectus dated May 1, 2013

Effective immediately, the Fund’s prospectus dated May 1, 2013 is supplemented by deleting the rows for Class R4 and Class R5 shares that appear within the table on page 11 under the heading Average Annual Total Return as of December 31, 2012 and replacing the rows in their entirety with the following:

	1 year	Life of Fund     (August 19, 2011)
Class R4 shares returns before taxes	31.32%	15.53%
Class R5 shares returns before taxes	31.40%	15.58%

COLUMBIA ACORN TRUST

Columbia Acorn European Fund^SM

(the “Fund”)

Supplement dated September 5, 2013

to the Prospectus dated May 1, 2013

Effective immediately, the Fund’s prospectus dated May 1, 2013 is supplemented by deleting the row for Class R5 shares that appears within the table on page 10 under the heading Average Annual Total Return as of December 31, 2012 and replacing the row in its entirety with the following:

	1 year	Life of Fund     (August 19, 2011)
Class R5 shares returns before taxes	25.67%	14.00%

Columbia Acorn Emerging Markets Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement [Text Block]

cat_SupplementTextblock

COLUMBIA ACORN TRUST

Columbia Acorn Emerging Markets Fund^SM

(the “Fund”)

Supplement dated September 5, 2013

to the Prospectus dated May 1, 2013

Effective immediately, the Fund’s prospectus dated May 1, 2013 is supplemented by deleting the rows for Class R4 and Class R5 shares that appear within the table on page 11 under the heading Average Annual Total Return as of December 31, 2012 and replacing the rows in their entirety with the following:

	1 year	Life of Fund     (August 19, 2011)
Class R4 shares returns before taxes	31.32%	15.53%
Class R5 shares returns before taxes	31.40%	15.58%

Columbia Acorn Emerging Markets Fund | Class R4 shares

Risk/Return:

rr_RiskReturnAbstract

1 year

rr_AverageAnnualReturnYear01

31.32%

Life of Fund

rr_AverageAnnualReturnSinceInception

15.53%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 19, 2011

Columbia Acorn Emerging Markets Fund | Class R5 shares

Risk/Return:

rr_RiskReturnAbstract

1 year

rr_AverageAnnualReturnYear01

31.40%

Life of Fund

rr_AverageAnnualReturnSinceInception

15.58%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 19, 2011

Columbia Acorn European Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement [Text Block]

cat_SupplementTextblock

COLUMBIA ACORN TRUST

Columbia Acorn European Fund^SM

(the “Fund”)

Supplement dated September 5, 2013

to the Prospectus dated May 1, 2013

Effective immediately, the Fund’s prospectus dated May 1, 2013 is supplemented by deleting the row for Class R5 shares that appears within the table on page 10 under the heading Average Annual Total Return as of December 31, 2012 and replacing the row in its entirety with the following:

	1 year	Life of Fund     (August 19, 2011)
Class R5 shares returns before taxes	25.67%	14.00%

Columbia Acorn European Fund | Class R5 shares

Risk/Return:

rr_RiskReturnAbstract

1 year

rr_AverageAnnualReturnYear01

25.67%

Life of Fund

rr_AverageAnnualReturnSinceInception

14.00%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 19, 2011