v2.4.1.9
Loans (Analysis of Impaired Loans) (Details) (Loans, Excluding Purchased Credit Impaired Loans [Member], USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment of Loans Collectively Measured for Contingency Provision $ 5,203,960us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment   $ 5,186,695us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Recorded Investment of Loans Individually Measured for Specific Impairment 27,096us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment   28,099us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Recorded Investment 25,893us-gaap_ImpairedFinancingReceivableRecordedInvestment   26,883us-gaap_ImpairedFinancingReceivableRecordedInvestment
Unpaid Principal Balance 31,634us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance   38,433us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Related Allowance 230us-gaap_ImpairedFinancingReceivableRelatedAllowance   241us-gaap_ImpairedFinancingReceivableRelatedAllowance
Average Recorded Investment Impaired Loans 27,596us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment 26,538us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment  
Interest Recognized on Impaired Loans 267us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod 336us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod  
Secured Loans [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment of Loans Collectively Measured for Contingency Provision 2,044,486us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   2,023,104us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment of Loans Individually Measured for Specific Impairment 10,873us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   10,524us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment 96us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   99us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 96us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   99us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Related Allowance 24us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   25us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Average Recorded Investment Impaired Loans 10,698us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 6,232us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Interest Recognized on Impaired Loans 7us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 17us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Unsecured Loans [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment of Loans Collectively Measured for Contingency Provision 79,219us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   80,091us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment of Loans Individually Measured for Specific Impairment 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   2us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment 0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   2us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   2us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Related Allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   2us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Average Recorded Investment Impaired Loans 1us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 31us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Interest Recognized on Impaired Loans 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
One-to-Four Family Residential [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment of Loans Collectively Measured for Contingency Provision 166,129us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   169,619us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment of Loans Individually Measured for Specific Impairment 4,178us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   2,145us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment 420us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   424us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 461us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   465us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Related Allowance 115us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   120us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Average Recorded Investment Impaired Loans 3,162us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 1,856us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Interest Recognized on Impaired Loans 13us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 13us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Commercial Land [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment of Loans Collectively Measured for Contingency Provision 192,972us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   189,779us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment of Loans Individually Measured for Specific Impairment 470us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment 0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Related Allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Average Recorded Investment Impaired Loans 235us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 111us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Interest Recognized on Impaired Loans 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Income Property Multifamily [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment of Loans Collectively Measured for Contingency Provision 1,307,556us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   1,295,650us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment of Loans Individually Measured for Specific Impairment 1,988us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   6,349us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment 0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Related Allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Average Recorded Investment Impaired Loans 4,168us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 6,436us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Interest Recognized on Impaired Loans 10us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 62us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Owner Occupied [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment of Loans Collectively Measured for Contingency Provision 839,157us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   835,895us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment of Loans Individually Measured for Specific Impairment 7,030us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   8,846us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment 578us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   582us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 578us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   582us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Related Allowance 24us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   27us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Average Recorded Investment Impaired Loans 7,938us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 10,140us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Interest Recognized on Impaired Loans 234us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 241us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Land And Acquisition [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment of Loans Collectively Measured for Contingency Provision 15,818us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   16,401us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment of Loans Individually Measured for Specific Impairment 980us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   109us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment 109us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   109us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 108us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   109us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Related Allowance 67us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   67us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Average Recorded Investment Impaired Loans 544us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 1,569us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Interest Recognized on Impaired Loans 1us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 1us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Residential Construction [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment of Loans Collectively Measured for Contingency Provision 104,752us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   98,521us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment of Loans Individually Measured for Specific Impairment 893us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment 0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Related Allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Average Recorded Investment Impaired Loans 446us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 0us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Interest Recognized on Impaired Loans 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Income Property Multifamily Construction [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment of Loans Collectively Measured for Contingency Provision 62,958us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   73,783us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment of Loans Individually Measured for Specific Impairment 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment 0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Related Allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Owner Occupied Construction [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment of Loans Collectively Measured for Contingency Provision 55,439us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   58,944us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment of Loans Individually Measured for Specific Impairment 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment 0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Related Allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Consumer Portfolio Segment [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment of Loans Collectively Measured for Contingency Provision 335,474us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   344,908us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment of Loans Individually Measured for Specific Impairment 684us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   124us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Recorded Investment 0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Related Allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Average Recorded Investment Impaired Loans 404us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 163us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Interest Recognized on Impaired Loans 2us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		 2us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		  
Impaired Loans With Recorded Allowance [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment 1,203us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ colb_ImpairedFinancingReceivableWithAllowanceAxis
= colb_ImpairedLoansWithRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   1,216us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ colb_ImpairedFinancingReceivableWithAllowanceAxis
= colb_ImpairedLoansWithRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 1,243us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ colb_ImpairedFinancingReceivableWithAllowanceAxis
= colb_ImpairedLoansWithRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   1,257us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ colb_ImpairedFinancingReceivableWithAllowanceAxis
= colb_ImpairedLoansWithRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Impaired Loans Without Recorded Allowance [Member] | Secured Loans [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment 10,777us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   10,425us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 12,986us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   12,410us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Impaired Loans Without Recorded Allowance [Member] | Unsecured Loans [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment 0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Impaired Loans Without Recorded Allowance [Member] | One-to-Four Family Residential [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment 3,758us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   1,721us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 4,220us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   2,370us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Impaired Loans Without Recorded Allowance [Member] | Commercial Land [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment 470us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 470us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Impaired Loans Without Recorded Allowance [Member] | Income Property Multifamily [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment 1,988us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   6,349us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 2,355us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   10,720us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Impaired Loans Without Recorded Allowance [Member] | Owner Occupied [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment 6,452us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   8,264us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 8,944us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   12,732us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Impaired Loans Without Recorded Allowance [Member] | Land And Acquisition [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment 871us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 871us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Impaired Loans Without Recorded Allowance [Member] | Residential Construction [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment 893us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 893us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Impaired Loans Without Recorded Allowance [Member] | Income Property Multifamily Construction [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment 0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Impaired Loans Without Recorded Allowance [Member] | Owner Occupied Construction [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment 0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Impaired Loans Without Recorded Allowance [Member] | Consumer Portfolio Segment [Member]      
Financing Receivable, Recorded Investment [Line Items]      
Recorded Investment 684us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   124us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember
Unpaid Principal Balance $ 895us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember		   $ 201us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ colb_ImpairedFinancingReceivableWithoutRelatedAllowanceAxis
= colb_ImpairedLoansWithoutRecordedAllowanceMember
/ colb_LoansByMajorCategoryAxis
= colb_LoansExcludingPurchasedCreditImpairedLoansMember