v2.4.1.9

Other Real Estate Owned (Summary of Other Real Estate Owned) (Details) (USD $) | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Other Real Estate Owned [Line Items] |  |
Balance, beginning of period | $ 22,190,000 us-gaap_RealEstateAcquiredThroughForeclosure | $ 35,927,000 us-gaap_RealEstateAcquiredThroughForeclosure
Transfers in | 4,692,000 colb_RealEstateAcquiredThroughForeclosureTransfersInNetOfWriteDowns | 5,751,000 colb_RealEstateAcquiredThroughForeclosureTransfersInNetOfWriteDowns
Valuation adjustments | (197,000)colb_TransferOtherRealEstateWriteDown | (1,580,000)colb_TransferOtherRealEstateWriteDown
Proceeds from Sale of OREO Property | 5,122,000 us-gaap_ProceedsFromSaleOfWhollyOwnedRealEstateAndRealEstateAcquiredInSettlementOfLoans | 11,205,000 us-gaap_ProceedsFromSaleOfWhollyOwnedRealEstateAndRealEstateAcquiredInSettlementOfLoans
Gain (loss) on sale of OREO | 1,736,000 us-gaap_GainsLossesOnSalesOfOtherRealEstate | 1,659,000 us-gaap_GainsLossesOnSalesOfOtherRealEstate
Total OREO, end of period | 23,299,000 us-gaap_RealEstateAcquiredThroughForeclosure | 30,552,000 us-gaap_RealEstateAcquiredThroughForeclosure
Mortgage Loans in Process of Foreclosure, Amount | 2,700,000 colb_MortgageLoansinProcessofForeclosureAmount |
One-to-Four Family Residential [Member] |  |
Other Real Estate Owned [Line Items] |  |
Total OREO, end of period | $ 2,100,000 us-gaap_RealEstateAcquiredThroughForeclosure / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember |

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- Definition Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process. + References No definition available. + Details
Name: | colb_MortgageLoansinProcessofForeclosureAmount
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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- 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 Transfer Other Real Estate Write Down + References No definition available. + Details
Name: | colb_TransferOtherRealEstateWriteDown
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition The net gain (loss) resulting from sales and other disposals of other real estate owned, increases (decreases) in the valuation allowance for foreclosed real estate, and write-downs of other real estate owned after acquisition or physical possession. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.14(d)) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 14 -Subparagraph d -Article 9 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition The cash inflow from proceeds From Sales of Wholly Owned Real Estate and Real Estate Acquired in Settlement of Loans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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 FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4437-111522 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 28 -Article 12 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 + Details
Name: | us-gaap_RealEstateAcquiredThroughForeclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |