v2.4.1.9

Allowance for Loan and Lease Losses and Unfunded Commitments and Letters of Credit (Analysis of Credit Quality of the Loan Portfolio) (Details) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014 | Mar. 31, 2014 | Dec. 31, 2013
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Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Allowance | $ 70,234 us-gaap_LoansAndLeasesReceivableAllowance | $ 69,569 us-gaap_LoansAndLeasesReceivableAllowance | $ 70,571 us-gaap_LoansAndLeasesReceivableAllowance | $ 72,454 us-gaap_LoansAndLeasesReceivableAllowance
Loans, net | 5,380,661 us-gaap_LoansAndLeasesReceivableNetReportedAmount | 5,375,809 us-gaap_LoansAndLeasesReceivableNetReportedAmount |  |
Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 5,231,056 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 5,214,794 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Loans and Leases Receivable, Allowance | 53,703 us-gaap_LoansAndLeasesReceivableAllowance / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 53,233 us-gaap_LoansAndLeasesReceivableAllowance / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Loans, net | 5,177,353 us-gaap_LoansAndLeasesReceivableNetReportedAmount / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 5,161,561 us-gaap_LoansAndLeasesReceivableNetReportedAmount / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 243,111 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 256,468 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Acquisition Accounting Valuation Discount on Purchased Credit Impaired Loans | 23,272 colb_AcquisitionAccountingValuationDiscountonPurchasedCreditImpairedLoans / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Loans and Leases Receivable, Allowance | 16,531 us-gaap_LoansAndLeasesReceivableAllowance / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 16,336 us-gaap_LoansAndLeasesReceivableAllowance / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Loans, net | 203,308 us-gaap_LoansAndLeasesReceivableNetReportedAmount / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 214,248 us-gaap_LoansAndLeasesReceivableNetReportedAmount / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Pass [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 5,122,539 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 5,086,653 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Special Mention [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 30,254 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 34,967 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Substandard [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 78,263 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 93,174 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Substandard [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 33,945 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 36,486 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Doubtful [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Doubtful [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Unlikely to be Collected Financing Receivable [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Unlikely to be Collected Financing Receivable [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Secured Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Allowance | 25,761 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember | 25,923 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember | 28,801 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember | 31,027 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember
Secured Loans [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 2,055,359 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 2,033,628 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Secured Loans [Member] | Pass [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 1,995,680 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 1,963,210 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Secured Loans [Member] | Special Mention [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 19,210 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 15,790 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Secured Loans [Member] | Substandard [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 40,469 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 54,628 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Secured Loans [Member] | Substandard [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 9,060 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Secured Loans [Member] | Doubtful [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Secured Loans [Member] | Doubtful [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Secured Loans [Member] | Unlikely to be Collected Financing Receivable [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_SecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Unsecured Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Allowance | 1,012 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember | 927 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember | 746 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember | 696 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember
Unsecured Loans [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 79,219 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 80,093 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Unsecured Loans [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 2,096 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 2,247 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Unsecured Loans [Member] | Pass [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 78,498 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 79,534 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Unsecured Loans [Member] | Pass [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 2,057 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Unsecured Loans [Member] | Special Mention [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Unsecured Loans [Member] | Special Mention [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Unsecured Loans [Member] | Substandard [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 721 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 559 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Unsecured Loans [Member] | Substandard [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 39 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Unsecured Loans [Member] | Doubtful [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Unsecured Loans [Member] | Doubtful [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Unsecured Loans [Member] | Unlikely to be Collected Financing Receivable [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Unsecured Loans [Member] | Unlikely to be Collected Financing Receivable [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_UnsecuredLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
One-to-Four Family Residential [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Allowance | 1,364 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember | 2,281 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember | 1,194 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember | 1,252 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember
One-to-Four Family Residential [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 170,307 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 171,764 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
One-to-Four Family Residential [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 31,127 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 31,981 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
One-to-Four Family Residential [Member] | Pass [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 162,448 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 163,914 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
One-to-Four Family Residential [Member] | Pass [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 27,881 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
One-to-Four Family Residential [Member] | Special Mention [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 1,465 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 55 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
One-to-Four Family Residential [Member] | Substandard [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 6,394 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 7,795 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
One-to-Four Family Residential [Member] | Doubtful [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
One-to-Four Family Residential [Member] | Doubtful [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount |  | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
One-to-Four Family Residential [Member] | Unlikely to be Collected Financing Receivable [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OneToFourFamilyResidentialMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Commercial Land [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Allowance | 827 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember | 799 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember | 579 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember | 489 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember
Commercial Land [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 193,442 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 189,779 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Commercial Land [Member] | Pass [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 187,519 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 183,701 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Commercial Land [Member] | Special Mention [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 3,459 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 4,217 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Commercial Land [Member] | Special Mention [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Commercial Land [Member] | Substandard [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 2,464 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 1,861 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Commercial Land [Member] | Substandard [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 1,668 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Commercial Land [Member] | Doubtful [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Commercial Land [Member] | Unlikely to be Collected Financing Receivable [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Commercial Land [Member] | Unlikely to be Collected Financing Receivable [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_CommercialLandMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Income Property Multifamily [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Allowance | 8,440 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember | 9,159 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember | 10,107 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember | 9,234 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember
Income Property Multifamily [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 1,309,544 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 1,301,999 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Income Property Multifamily [Member] | Pass [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 1,301,779 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 1,287,729 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Income Property Multifamily [Member] | Pass [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 45,298 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Income Property Multifamily [Member] | Special Mention [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 3,517 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 5,885 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Income Property Multifamily [Member] | Special Mention [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Income Property Multifamily [Member] | Substandard [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 4,248 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 8,385 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Income Property Multifamily [Member] | Substandard [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 12,031 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 7,186 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Income Property Multifamily [Member] | Doubtful [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Income Property Multifamily [Member] | Doubtful [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Income Property Multifamily [Member] | Unlikely to be Collected Financing Receivable [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Owner Occupied [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Allowance | 5,612 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedMember | 5,007 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedMember | 4,560 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedMember | 3,605 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedMember
Owner Occupied [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 846,187 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 844,741 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Owner Occupied [Member] | Pass [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 828,244 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 825,694 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Owner Occupied [Member] | Special Mention [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 1,757 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 7,876 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Owner Occupied [Member] | Special Mention [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount |  | 346 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Owner Occupied [Member] | Substandard [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Owner Occupied [Member] | Doubtful [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Owner Occupied [Member] | Doubtful [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Owner Occupied [Member] | Unlikely to be Collected Financing Receivable [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Owner Occupied [Member] | Unlikely to be Collected Financing Receivable [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Land And Acquisition [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Allowance | 1,026 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_LandAndAcquisitionMember | 1,197 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_LandAndAcquisitionMember | 580 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_LandAndAcquisitionMember | 610 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_LandAndAcquisitionMember
Land And Acquisition [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Land And Acquisition [Member] | Pass [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 16,180 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_LandAndAcquisitionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 15,307 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_LandAndAcquisitionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Land And Acquisition [Member] | Special Mention [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 166 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_LandAndAcquisitionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 167 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_LandAndAcquisitionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Land And Acquisition [Member] | Special Mention [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Land And Acquisition [Member] | Substandard [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 452 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_LandAndAcquisitionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 1,036 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_LandAndAcquisitionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Land And Acquisition [Member] | Substandard [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Land And Acquisition [Member] | Doubtful [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Land And Acquisition [Member] | Doubtful [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Land And Acquisition [Member] | Unlikely to be Collected Financing Receivable [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Land And Acquisition [Member] | Unlikely to be Collected Financing Receivable [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Residential Construction [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Allowance | 1,790 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember | 1,860 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember | 696 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember | 822 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember
Residential Construction [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 105,645 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 98,521 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Residential Construction [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount |  | 1,845 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Residential Construction [Member] | Pass [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 103,257 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 96,031 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Residential Construction [Member] | Pass [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 732 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 741 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Residential Construction [Member] | Special Mention [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 680 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 909 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Residential Construction [Member] | Special Mention [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Residential Construction [Member] | Substandard [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 1,708 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 1,581 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Residential Construction [Member] | Substandard [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount |  | 1,104 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Residential Construction [Member] | Doubtful [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Residential Construction [Member] | Doubtful [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount |  | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Residential Construction [Member] | Unlikely to be Collected Financing Receivable [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Residential Construction [Member] | Unlikely to be Collected Financing Receivable [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount |  | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_ResidentialConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Income Property Multifamily Construction [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Allowance | 827 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember | 622 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember | 320 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember | 285 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember
Income Property Multifamily Construction [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 62,958 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 73,783 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Income Property Multifamily Construction [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount |  | 1,662 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Income Property Multifamily Construction [Member] | Pass [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 62,958 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 73,783 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Income Property Multifamily Construction [Member] | Special Mention [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Income Property Multifamily Construction [Member] | Special Mention [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Income Property Multifamily Construction [Member] | Substandard [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Income Property Multifamily Construction [Member] | Substandard [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 224 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Income Property Multifamily Construction [Member] | Doubtful [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Income Property Multifamily Construction [Member] | Unlikely to be Collected Financing Receivable [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Income Property Multifamily Construction [Member] | Unlikely to be Collected Financing Receivable [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount |  | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_IncomePropertyMultifamilyConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Owner Occupied Construction [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Allowance | 499 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember | 434 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember | 154 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember | 58 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember
Owner Occupied Construction [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 55,439 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 58,944 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Owner Occupied Construction [Member] | Pass [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 54,563 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 58,055 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Owner Occupied Construction [Member] | Special Mention [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Owner Occupied Construction [Member] | Special Mention [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Owner Occupied Construction [Member] | Substandard [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 876 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 889 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Owner Occupied Construction [Member] | Substandard [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount |  | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Owner Occupied Construction [Member] | Doubtful [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Owner Occupied Construction [Member] | Unlikely to be Collected Financing Receivable [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Owner Occupied Construction [Member] | Unlikely to be Collected Financing Receivable [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = colb_OwnerOccupiedConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |  |
Consumer Portfolio Segment [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Allowance | 2,835 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 3,180 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 2,637 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 2,547 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Consumer Portfolio Segment [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 336,158 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 345,032 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Consumer Portfolio Segment [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 25,390 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember | 26,814 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Consumer Portfolio Segment [Member] | Pass [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 331,413 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 339,695 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Consumer Portfolio Segment [Member] | Pass [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount |  | 24,037 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember / colb_LoansByMajorCategoryAxis = colb_PurchasedCreditImpairedLoansMember |  |
Consumer Portfolio Segment [Member] | Special Mention [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 68 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Consumer Portfolio Segment [Member] | Substandard [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 4,745 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 5,269 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Consumer Portfolio Segment [Member] | Substandard [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Consumer Portfolio Segment [Member] | Doubtful [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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Consumer Portfolio Segment [Member] | Unlikely to be Collected Financing Receivable [Member] | Loans, Excluding Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and Leases Receivable, Gross, Carrying Amount | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_UnlikelyToBeCollectedFinancingReceivableMember / colb_LoansByMajorCategoryAxis = colb_LoansExcludingPurchasedCreditImpairedLoansMember |  |
Consumer Portfolio Segment [Member] | Unlikely to be Collected Financing Receivable [Member] | Purchased Credit Impaired Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
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