v2.4.1.9
Covered Assets and FDIC Loss-sharing Asset (Narrative) (Details) (USD $)
 3 Months Ended
Mar. 31, 2015
Covered Assets And FDIC Loss Sharing Asset [Line Items]  
Amount of Estimated Clawback Liability $ 4,199,000colb_AmountOfEstimatedClawbackLiability
Payment Of Clawback If Losses Less Than Stated Levels, Period After Acquisition 10 years 45 days
Federal deposit insurance corporation loss-sharing indemnified assets 10,600,000colb_FederalDepositInsuranceCorporationLossSharingIndemnifiedAssets
Federal deposit insurance corporation loss-sharing indemnified assets receivable $ 4,000,000colb_FederalDepositInsuranceCorporationLossSharingIndemnifiedAssetsReceivable
Maximum [Member]  
Covered Assets And FDIC Loss Sharing Asset [Line Items]  
Loss Sharing Agreement Effective Years 10 years
Loss Recovery Provision Effective Years 10 years
Minimum [Member]  
Covered Assets And FDIC Loss Sharing Asset [Line Items]  
Loss Sharing Agreement Effective Years 5 years
Loss Recovery Provision Effective Years 8 years
Covered Loans [Member]  
Covered Assets And FDIC Loss Sharing Asset [Line Items]  
Percentage of loss shared by FDIC 80.00%colb_PercentageOfLossSharedByFdic
/ colb_LoansByMajorCategoryAxis
= colb_CoveredLoansMember
FDIC Percentage Of Loss Recoveries 80.00%colb_FdicPercentageOfLossRecoveries
/ colb_LoansByMajorCategoryAxis
= colb_CoveredLoansMember
Percentage of loss shared by FDIC When Loss Share Thresholds Met 95.00%colb_PercentageOfLossSharedByFdicWhenLossShareThresholdsMet
/ colb_LoansByMajorCategoryAxis
= colb_CoveredLoansMember
Percentage Of Loss Recoveries Shared By FDIC When Loss Share Thresholds Met 95.00%colb_PercentageOfLossRecoveriesSharedByFdicWhenLossShareThresholdsMet
/ colb_LoansByMajorCategoryAxis
= colb_CoveredLoansMember