v2.4.1.9
Allowance for Loan and Lease Losses and Unfunded Commitments and Letters of Credit (Allowance for Loan and Lease Losses) (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance $ 69,569us-gaap_LoansAndLeasesReceivableAllowance $ 72,454us-gaap_LoansAndLeasesReceivableAllowance
Charged-offs (6,425)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs (6,463)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
Recoveries 5,881us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts 2,658us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
Provision for loan and lease losses 1,209us-gaap_ProvisionForLoanAndLeaseLosses [1] 1,922us-gaap_ProvisionForLoanAndLeaseLosses [1]
Ending balance 70,234us-gaap_LoansAndLeasesReceivableAllowance 70,571us-gaap_LoansAndLeasesReceivableAllowance
Specific Reserve 230colb_LoanAndLeaseLossesSpecificReserve 1,793colb_LoanAndLeaseLossesSpecificReserve
General Allocation 70,004colb_LoanAndLeaseLossesGeneralAllocation 68,778colb_LoanAndLeaseLossesGeneralAllocation
Secured Loans [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 25,923us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember		 31,027us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
Charged-offs (1,386)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember		 (198)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
Recoveries 512us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember		 448us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
Provision for loan and lease losses 712us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember		 (2,476)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
Ending balance 25,761us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember		 28,801us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
Specific Reserve 24colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember		 1,521colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
General Allocation 25,737colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember		 27,280colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_SecuredLoansMember
Unsecured Loans [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 927us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember		 696us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
Charged-offs (40)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember		 (35)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
Recoveries 106us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember		 42us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
Provision for loan and lease losses 19us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember		 43us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
Ending balance 1,012us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember		 746us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
Specific Reserve 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember		 27colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
General Allocation 1,012colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember		 719colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_UnsecuredLoansMember
One-to-Four Family Residential [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 2,281us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember		 1,252us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
Charged-offs (8)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember		 (207)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
Recoveries 12us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember		 28us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
Provision for loan and lease losses (921)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember		 121us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
Ending balance 1,364us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember		 1,194us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
Specific Reserve 115colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember		 133colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
General Allocation 1,249colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember		 1,061colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OneToFourFamilyResidentialMember
Commercial Land [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 799us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember		 489us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
Charged-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember		 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
Recoveries 0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember		 17us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
Provision for loan and lease losses 28us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember		 73us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
Ending balance 827us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember		 579us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
Specific Reserve 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember		 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
General Allocation 827colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember		 579colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_CommercialLandMember
Income Property Multifamily [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 9,159us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember		 9,234us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
Charged-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember		 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
Recoveries 3,252us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember		 13us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
Provision for loan and lease losses (3,971)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember		 860us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
Ending balance 8,440us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember		 10,107us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
Specific Reserve 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember		 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
General Allocation 8,440colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember		 10,107colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyMember
Owner Occupied [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 5,007us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember		 3,605us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
Charged-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember		 (1,023)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
Recoveries 9us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember		 9us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
Provision for loan and lease losses 596us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember		 1,969us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
Ending balance 5,612us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember		 4,560us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
Specific Reserve 24colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember		 38colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
General Allocation 5,588colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember		 4,522colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedMember
Land And Acquisition [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 1,197us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember		 610us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
Charged-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember		 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
Recoveries 2us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember		 39us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
Provision for loan and lease losses (173)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember		 (69)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
Ending balance 1,026us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember		 580us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
Specific Reserve 67colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember		 71colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
General Allocation 959colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember		 509colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_LandAndAcquisitionMember
Residential Construction [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 1,860us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember		 822us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
Charged-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember		 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
Recoveries 26us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember		 3us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
Provision for loan and lease losses (96)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember		 (129)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
Ending balance 1,790us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember		 696us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
Specific Reserve 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember		 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
General Allocation 1,790colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember		 696colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_ResidentialConstructionMember
Income Property Multifamily Construction [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 622us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember		 285us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
Charged-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember		 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
Recoveries 3us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember		 0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
Provision for loan and lease losses 202us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember		 35us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
Ending balance 827us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember		 320us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
Specific Reserve 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember		 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
General Allocation 827colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember		 320colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_IncomePropertyMultifamilyConstructionMember
Owner Occupied Construction [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 434us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember		 58us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
Charged-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember		 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
Recoveries 0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember		 0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
Provision for loan and lease losses 65us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember		 96us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
Ending balance 499us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember		 154us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
Specific Reserve 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember		 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
General Allocation 499colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember		 154colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_OwnerOccupiedConstructionMember
Consumer Portfolio Segment [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 3,180us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember		 2,547us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Charged-offs (891)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember		 (727)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Recoveries 273us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember		 253us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Provision for loan and lease losses 273us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember		 564us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Ending balance 2,835us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember		 2,637us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Specific Reserve 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember		 3colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
General Allocation 2,835colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember		 2,634colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Purchased Credit Impaired Loans [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 16,336us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember		 20,174us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember
Charged-offs (4,100)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember		 (4,273)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember
Recoveries 1,686us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember		 1,806us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember
Provision for loan and lease losses 2,609us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember		 2,422us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember
Ending balance 16,531us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember		 20,129us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember
Specific Reserve 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember		 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember
General Allocation 16,531colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember		 20,129colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= colb_PurchasedCreditImpairedLoansMember
Unallocated Financing Receivables [Member]    
Allowance for Loan and Lease Losses [Roll Forward]    
Beginning balance 1,844us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember		 1,655us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
Charged-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember		 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
Recoveries 0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember		 0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
Provision for loan and lease losses 1,866us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember		 (1,587)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
Ending balance 3,710us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember		 68us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
Specific Reserve 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember		 0colb_LoanAndLeaseLossesSpecificReserve
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
General Allocation $ 3,710colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember		 $ 68colb_LoanAndLeaseLossesGeneralAllocation
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
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