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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Document Type dei_DocumentType Other
Document Period End Date dei_DocumentPeriodEndDate Dec. 31, 2011
Registrant Name dei_EntityRegistrantName COLUMBIA ACORN TRUST
Central Index Key dei_EntityCentralIndexKey 0000002110
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Aug. 28, 2012
Document Effective Date dei_DocumentEffectiveDate Aug. 28, 2012
Prospectus Date rr_ProspectusDate Aug. 28, 2012
Supplement Text Block columbia_SupplementTextBlock

COLUMBIA ACORN TRUST
Columbia Acorn Select℠
(the "Fund")

Supplement dated August 28, 2012
to the Prospectuses dated May 1, 2012
(Columbia Acorn Select℠)
  
Risk/Return: rr_RiskReturnAbstract  
Supplement Text Block columbia_SupplementTextBlock
Effective immediately, the Fund's prospectuses dated May 1, 2012 are supplemented by adding the following after the third full paragraph that appears under the heading "Principal Investment Strategies:"
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund takes advantage of the Investment Manager's research and stock-picking capabilities to invest in a limited number of companies (generally between 30-60), offering the potential to provide above-average growth over time.