v2.4.1.9

Covered Assets and FDIC Loss-sharing Asset (FDIC Loss-sharing Asset) (Details) (USD $) In Thousands, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2015 | Mar. 31, 2014
Covered Assets And FDIC Loss Sharing Asset [Line Items] |  |
Balance at beginning of period | $ 15,174 us-gaap_FDICIndemnificationAsset | $ 39,846 us-gaap_FDICIndemnificationAsset
Cash received from the FDIC | (659)colb_FdicLossSharingAssetCashPaymentsReceived | 1,678 colb_FdicLossSharingAssetCashPaymentsReceived
FDIC reimbursable losses, net | (21)colb_FdicLossSharingAssetNetReimbursableLosses | 132 colb_FdicLossSharingAssetNetReimbursableLosses
Amortization, net | (2,294)colb_FdicLossSharingAssetAmortizationNet | (6,452)colb_FdicLossSharingAssetAmortizationNet
Impairment | 1,532 colb_FDICLosssharingAssetImpairmentRecaptureofLoans | 1,938 colb_FDICLosssharingAssetImpairmentRecaptureofLoans
Sale of other real estate | (420)colb_FdicLossSharingAssetDisposals | (756)colb_FdicLossSharingAssetDisposals
Write-downs of other real estate | 1,071 colb_FdicLossSharingAssetWriteDownsOfOtherRealEstate | 516 colb_FdicLossSharingAssetWriteDownsOfOtherRealEstate
Other | 261 colb_FdicLossSharingAssetOther | (65)colb_FdicLossSharingAssetOther
Balance at end of period | 14,644 us-gaap_FDICIndemnificationAsset | 36,837 us-gaap_FDICIndemnificationAsset
Amount of Estimated Clawback Liability | 4,199 colb_AmountOfEstimatedClawbackLiability |
Non-Single Family Covered Assets | 160,668 colb_NonSingleFamilyCoveredAssets |
Single Family Covered Assets | 45,186 colb_SingleFamilyCoveredAssets |
Columbia River Bank [Member] |  |
Covered Assets And FDIC Loss Sharing Asset [Line Items] |  |
Balance at end of period | 2,124 us-gaap_FDICIndemnificationAsset / us-gaap_BusinessAcquisitionAxis = colb_ColumbiaRiverBankMember |
Amount of Estimated Clawback Liability | 4,063 colb_AmountOfEstimatedClawbackLiability / us-gaap_BusinessAcquisitionAxis = colb_ColumbiaRiverBankMember |
Non-Single Family Covered Assets | 107,135 colb_NonSingleFamilyCoveredAssets / us-gaap_BusinessAcquisitionAxis = colb_ColumbiaRiverBankMember |
Single Family Covered Assets | 9,994 colb_SingleFamilyCoveredAssets / us-gaap_BusinessAcquisitionAxis = colb_ColumbiaRiverBankMember |
American Marine Bank [Member] |  |
Covered Assets And FDIC Loss Sharing Asset [Line Items] |  |
Balance at end of period | 4,824 us-gaap_FDICIndemnificationAsset / us-gaap_BusinessAcquisitionAxis = colb_AmericanMarineBankMember |
Amount of Estimated Clawback Liability | 136 colb_AmountOfEstimatedClawbackLiability / us-gaap_BusinessAcquisitionAxis = colb_AmericanMarineBankMember |
Non-Single Family Covered Assets | 16,914 colb_NonSingleFamilyCoveredAssets / us-gaap_BusinessAcquisitionAxis = colb_AmericanMarineBankMember |
Single Family Covered Assets | 26,391 colb_SingleFamilyCoveredAssets / us-gaap_BusinessAcquisitionAxis = colb_AmericanMarineBankMember |
Summit Bank [Member] |  |
Covered Assets And FDIC Loss Sharing Asset [Line Items] |  |
Balance at end of period | 4,162 us-gaap_FDICIndemnificationAsset / us-gaap_BusinessAcquisitionAxis = colb_SummitBankMember |
Amount of Estimated Clawback Liability | 0 colb_AmountOfEstimatedClawbackLiability / us-gaap_BusinessAcquisitionAxis = colb_SummitBankMember |
Non-Single Family Covered Assets | 13,856 colb_NonSingleFamilyCoveredAssets / us-gaap_BusinessAcquisitionAxis = colb_SummitBankMember |
Single Family Covered Assets | 6,322 colb_SingleFamilyCoveredAssets / us-gaap_BusinessAcquisitionAxis = colb_SummitBankMember |
First Heritage Bank [Member] |  |
Covered Assets And FDIC Loss Sharing Asset [Line Items] |  |
Balance at end of period | 3,534 us-gaap_FDICIndemnificationAsset / us-gaap_BusinessAcquisitionAxis = colb_FirstHeritageBankMember |
Amount of Estimated Clawback Liability | 0 colb_AmountOfEstimatedClawbackLiability / us-gaap_BusinessAcquisitionAxis = colb_FirstHeritageBankMember |
Non-Single Family Covered Assets | 22,763 colb_NonSingleFamilyCoveredAssets / us-gaap_BusinessAcquisitionAxis = colb_FirstHeritageBankMember |
Single Family Covered Assets | $ 2,479 colb_SingleFamilyCoveredAssets / us-gaap_BusinessAcquisitionAxis = colb_FirstHeritageBankMember |

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

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

X
- Definition FDIC Loss-sharing Asset, Amortization, Net + References No definition available. + Details
Name: | colb_FdicLossSharingAssetAmortizationNet
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition FDIC Loss-sharing Asset, Cash Payments Received + References No definition available. + Details
Name: | colb_FdicLossSharingAssetCashPaymentsReceived
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition FDIC Loss-sharing Asset, Disposals + References No definition available. + Details
Name: | colb_FdicLossSharingAssetDisposals
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition FDIC Loss-sharing Asset, Impairment (Recapture) of Loans + References No definition available. + Details
Name: | colb_FDICLosssharingAssetImpairmentRecaptureofLoans
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition FDIC Loss-sharing Asset, Net Reimbursable Losses + References No definition available. + Details
Name: | colb_FdicLossSharingAssetNetReimbursableLosses
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition FDIC Loss-sharing Asset, Other + References No definition available. + Details
Name: | colb_FdicLossSharingAssetOther
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition FDIC Loss-sharing Asset, Write-downs of Other Real Estate + References No definition available. + Details
Name: | colb_FdicLossSharingAssetWriteDownsOfOtherRealEstate
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Non-Single Family Covered Assets + References No definition available. + Details
Name: | colb_NonSingleFamilyCoveredAssets
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Single Family Covered Assets + References No definition available. + Details
Name: | colb_SingleFamilyCoveredAssets
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Carrying amount of receivable assets originating from the indemnification agreement with the Federal Deposit Insurance Corporation (FDIC), in which the FDIC is to partially cover losses. + References No definition available. + Details
Name: | us-gaap_FDICIndemnificationAsset
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=colb_AmericanMarineBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=colb_ColumbiaRiverBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=colb_FirstHeritageBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=colb_SummitBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |