v2.4.1.9

Covered Assets and FDIC Loss-sharing Asset (Narrative) (Details) (USD $) | 3 Months Ended
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Mar. 31, 2015
Covered Assets And FDIC Loss Sharing Asset [Line Items] |
Amount of Estimated Clawback Liability | $ 4,199,000 colb_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 | 10,600,000 colb_FederalDepositInsuranceCorporationLossSharingIndemnifiedAssets
Federal deposit insurance corporation loss-sharing indemnified assets receivable | $ 4,000,000 colb_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

X
- Definition Amount of estimated clawback liability + References No definition available. + Details
Name: | colb_AmountOfEstimatedClawbackLiability
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

X
- Definition FDIC Percentage Of Loss Recoveries + References No definition available. + Details
Name: | colb_FdicPercentageOfLossRecoveries
Namespace Prefix: | colb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Federal deposit insurance corporation loss-sharing indemnified assets + References No definition available. + Details
Name: | colb_FederalDepositInsuranceCorporationLossSharingIndemnifiedAssets
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Federal deposit insurance corporation loss-sharing indemnified assets receivable + References No definition available. + Details
Name: | colb_FederalDepositInsuranceCorporationLossSharingIndemnifiedAssetsReceivable
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Loss Recovery Provision Effective Years + References No definition available. + Details
Name: | colb_LossRecoveryProvisionEffectiveYears
Namespace Prefix: | colb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Loss Sharing Agreement Effective Years + References No definition available. + Details
Name: | colb_LossSharingAgreementEffectiveYears
Namespace Prefix: | colb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Payment Of Clawback If Losses Less Than Stated Levels, Period After Acquisition + References No definition available. + Details
Name: | colb_PaymentOfClawbackIfLossesLessThanStatedLevelsPeriodAfterAcquisition
Namespace Prefix: | colb_
Data Type: | us-types:durationStringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage Of Loss Recoveries Shared By FDIC When Loss Share Thresholds Met + References No definition available. + Details
Name: | colb_PercentageOfLossRecoveriesSharedByFdicWhenLossShareThresholdsMet
Namespace Prefix: | colb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage of loss shared by FDIC + References No definition available. + Details
Name: | colb_PercentageOfLossSharedByFdic
Namespace Prefix: | colb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage of loss shared by FDIC When Loss Share Thresholds Met + References No definition available. + Details
Name: | colb_PercentageOfLossSharedByFdicWhenLossShareThresholdsMet
Namespace Prefix: | colb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | colb_LoansByMajorCategoryAxis=colb_CoveredLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |