v2.4.0.6

Covered Assets and FDIC Loss-sharing Asset (Covered OREO at Carrying Value) (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2011 | Dec. 31, 2010
Covered Assets And FDIC Loss Sharing Asset [Line Items] |  |
Balance, beginning of period | $ 45,434 |
Transfers in, write-downs | 2,564 | 2,087
Balance, end of period | 51,019 | 45,434
Covered Loans [Member] |  |
Covered Assets And FDIC Loss Sharing Asset [Line Items] |  |
Balance, beginning of period | 14,443 | 0
Established through acquisitions | 10,387 | 17,394
Transfers in, net of write-downs ($2,564 and $2,087, respectively) | 15,522 | 10,858
OREO improvements | 5 | 85
Additional OREO write-downs | (666) | (1,182)
Proceeds from sale of OREO property | (20,619) | (17,890)
Gain on sale of OREO | 9,054 | 5,178
Balance, end of period | $ 28,126 | $ 14,443

X
- Definition Capital improvements on foreclosed real estate acquired. + References No definition available. + Details
Name: | colb_CapitalImprovementsOnForeclosedRealEstateAcquired
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Definition Covered Oreo write downs. + References No definition available. + Details
Name: | colb_CoveredOreoWriteDowns
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Covered real estate acquired through foreclosure. + References No definition available. + Details
Name: | colb_CoveredRealEstateAcquiredThroughForeclosure
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Gain on sale of covered oreo. + References No definition available. + Details
Name: | colb_GainOnSaleOfCoveredOreo
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Proceeds from sale of covered foreclosed assets. + References No definition available. + Details
Name: | colb_ProceedsFromSaleOfCoveredForeclosedAssets
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Real Estate Acquired Through Foreclosure Transfers In Net Of Write Downs + References No definition available. + Details
Name: | colb_RealEstateAcquiredThroughForeclosureTransfersInNetOfWriteDowns
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Writedowns Previously Recorded On Transfer In Of Real Estate Acquired Through Foreclosure + References No definition available. + Details
Name: | colb_WritedownsPreviouslyRecordedOnTransferInOfRealEstateAcquiredThroughForeclosure
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-DEP -Chapter 11 -Paragraph 2, 9, 10, 11 -IssueDate 2006-05-01 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6375948&loc=d3e4437-111522 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph c -Subparagraph Schedule III -Article 5 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 28 -Article 12 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Statement of Position (SOP) -Number 01-6 -Paragraph 13 -Subparagraph f -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_RealEstateAcquiredThroughForeclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant