v2.4.1.9

Loans (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015 contract	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans to related parties	$ 12,700,000us-gaap_LoansAndLeasesReceivableRelatedParties	$ 13,200,000us-gaap_LoansAndLeasesReceivableRelatedParties
Loans and Leases Receivable, Related Parties, Additions	0us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions
Repayments on related party loans	430,000us-gaap_LoansAndLeasesReceivableRelatedPartiesCollections
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Loans Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	1,300,000,000us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1 / us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralAxis = us-gaap_LoansReceivableMember	1,080,000,000us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1 / us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralAxis = us-gaap_LoansReceivableMember
Federal Reserve Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	$ 47,000,000colb_FederalReserveBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged / us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralAxis = us-gaap_LoansReceivableMember	$ 46,000,000colb_FederalReserveBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged / us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralAxis = us-gaap_LoansReceivableMember

X

- Definition

Federal Reserve Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged

+ References

No definition available.

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- Definition

Amount of the collateral pledged in support of federal home loan bank advances outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822



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- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

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- Definition

For an unclassified balance sheet, reflects the carrying amount of unpaid loan amounts due from related parties at the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

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Reflects the amount of new advances made to related parties in the form of loan and lease receivables.

+ References

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Reflects the amount of collections received from related parties to reduce the carrying amounts of loans and leases receivable due from them.

+ References

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-Name Accounting Standards Codification

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