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

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