v2.4.0.6

Allowance for Noncovered Loan and Lease Losses and Unfunded Commitments and Letters of Credit (Changes in the Allowance for Unfunded Commitments and Letters of Credit) (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Allowance For Loan And Lease Losses And Unfunded Loan Commitments And Letters Of Credit |  |  |
Beginning balance | $ 1,165 | $ 775 | $ 500
Net changes in the allowance for unfunded commitments and letters of credit | 370 | 390 | 275
Ending balance | $ 1,535 | $ 1,165 | $ 775

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- Details
Name: | colb_AllowanceForLoanAndLeaseLossesAndUnfundedLoanCommitmentsAndLettersOfCredit
Namespace Prefix: | colb_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Allowance for Loan and Lease Losses, Net Changes In Unfunded Commitments and Letters Of Credit Allowance + References No definition available. + Details
Name: | colb_AllowanceForLoanAndLeaseLossesNetChangesInUnfundedCommitmentsAndLettersOfCreditAllowance
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Allowance For Unfunded Loan Commitments And Letters Of Credit + References No definition available. + Details
Name: | colb_AllowanceForUnfundedLoanCommitmentsAndLettersOfCredit
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant