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Loans Receivable (excluding Covered Loans) - Schedule of Loans Receivable (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Sep. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	$ 8,793,428us-gaap_LoansAndLeasesReceivableGrossCarryingAmount	$ 8,669,717us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Ratio of type of loan to total loans receivable	100.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans	100.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans
Allowance for probable losses	108,700us-gaap_FinancingReceivableAllowanceForCreditLosses	112,347us-gaap_FinancingReceivableAllowanceForCreditLosses	116,741us-gaap_FinancingReceivableAllowanceForCreditLosses
Loans in process	370,655us-gaap_LoansAndLeasesReceivableLoansInProcess	346,172us-gaap_LoansAndLeasesReceivableLoansInProcess
Discount on acquired loans	22,535wfsl_DiscountOnAcquiredLoans	25,391wfsl_DiscountOnAcquiredLoans
Deferred net origination fees	37,621us-gaap_LoansAndLeasesReceivableDeferredIncome	37,485us-gaap_LoansAndLeasesReceivableDeferredIncome
Charges against loans receivable	539,511wfsl_LoansAndLeasesReceivableChargesToAllowanceLoansInProcessAndDeferredFees	521,395wfsl_LoansAndLeasesReceivableChargesToAllowanceLoansInProcessAndDeferredFees
Loans receivable, net	8,253,917us-gaap_LoansAndLeasesReceivableNetReportedAmount	8,148,322us-gaap_LoansAndLeasesReceivableNetReportedAmount
Single-Family Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	5,619,694us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	5,572,244us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Ratio of type of loan to total loans receivable	64.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	64.20%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Allowance for probable losses	55,495us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	62,763us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	64,184us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Construction - Speculative [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	152,450us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember	140,060us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember
Ratio of type of loan to total loans receivable	1.70%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember	1.60%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember
Allowance for probable losses	5,451us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember	6,742us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember	8,407us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember
Construction - Custom [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	377,561us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember	385,824us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember
Ratio of type of loan to total loans receivable	4.30%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember	4.50%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember
Allowance for probable losses	965us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember	1,695us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember	882us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember
Land - Acquisition & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	86,405us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	80,359us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Ratio of type of loan to total loans receivable	1.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	0.90%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Allowance for probable losses	6,671us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	5,592us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	9,165us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Land - Consumer Lot Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	106,988us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember	111,130us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember
Ratio of type of loan to total loans receivable	1.20%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember	1.30%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember
Allowance for probable losses	3,113us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember	3,077us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember	3,552us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember
Multi-Family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	980,706us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	920,285us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember
Ratio of type of loan to total loans receivable	11.20%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	10.60%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember
Allowance for probable losses	4,500us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	4,248us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	3,816us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	749,856us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	752,957us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Ratio of type of loan to total loans receivable	8.50%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	8.70%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Allowance for probable losses	5,872us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	7,548us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	5,595us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial & Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	453,418us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	434,088us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember
Ratio of type of loan to total loans receivable	5.20%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	5.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember
Allowance for probable losses	23,328us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	16,527us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	16,614us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember
HELOC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	134,998us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	134,455us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember
Ratio of type of loan to total loans receivable	1.50%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	1.60%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember
Allowance for probable losses	892us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	928us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	1,002us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	131,352us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	138,315us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Ratio of type of loan to total loans receivable	1.40%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	1.60%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Allowance for probable losses	2,413us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	3,227us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	3,524us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Non-Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	8,538,202us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember	8,409,022us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember
Ratio of type of loan to total loans receivable	97.30%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember	97.20%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember
Non-Acquired Loans [Member] | Single-Family Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	5,608,208us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	5,560,203us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Ratio of type of loan to total loans receivable	63.90%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	64.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Non-Acquired Loans [Member] | Construction - Speculative [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	152,450us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember	140,060us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember
Ratio of type of loan to total loans receivable	1.70%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember	1.60%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember
Non-Acquired Loans [Member] | Construction - Custom [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	377,561us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember	385,824us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember
Ratio of type of loan to total loans receivable	4.30%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember	4.50%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember
Non-Acquired Loans [Member] | Land - Acquisition & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	84,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	77,832us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Ratio of type of loan to total loans receivable	1.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	0.90%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Non-Acquired Loans [Member] | Land - Consumer Lot Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	104,492us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember	108,623us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember
Ratio of type of loan to total loans receivable	1.20%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember	1.30%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember
Non-Acquired Loans [Member] | Multi-Family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	977,752us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	917,286us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember
Ratio of type of loan to total loans receivable	11.20%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	10.60%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember
Non-Acquired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	597,436us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	591,336us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Ratio of type of loan to total loans receivable	6.80%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	6.90%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Non-Acquired Loans [Member] | Commercial & Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	391,327us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	379,226us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember
Ratio of type of loan to total loans receivable	4.50%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	4.40%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember
Non-Acquired Loans [Member] | HELOC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	118,047us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	116,042us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember
Ratio of type of loan to total loans receivable	1.30%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	1.40%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember
Non-Acquired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	126,929us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	132,590us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Ratio of type of loan to total loans receivable	1.40%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	1.50%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	180,572us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember	181,355us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember
Ratio of type of loan to total loans receivable	1.90%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember	2.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember
Acquired Loans [Member] | Single-Family Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	11,163us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	11,716us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Ratio of type of loan to total loans receivable	0.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	0.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Acquired Loans [Member] | Land - Acquisition & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	872us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	905us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Acquired Loans [Member] | Land - Consumer Lot Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	2,496us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember	2,507us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember
Acquired Loans [Member] | Multi-Family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	2,954us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	2,999us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember
Acquired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	92,133us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	97,898us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Ratio of type of loan to total loans receivable	1.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	1.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Acquired Loans [Member] | Commercial & Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	58,836us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	51,386us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember
Ratio of type of loan to total loans receivable	0.70%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	0.60%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember
Acquired Loans [Member] | HELOC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	7,749us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	8,274us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember
Ratio of type of loan to total loans receivable	0.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	0.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember
Acquired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	4,369us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	5,670us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	0.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Credit Impaired Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	74,654us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember	79,340us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember
Ratio of type of loan to total loans receivable	0.80%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember	0.80%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember
Credit Impaired Acquired Loans [Member] | Single-Family Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	323us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	325us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Credit Impaired Acquired Loans [Member] | Land - Acquisition & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	1,533us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	1,622us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Credit Impaired Acquired Loans [Member] | Multi-Family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember
Credit Impaired Acquired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	60,287us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	63,723us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Ratio of type of loan to total loans receivable	0.70%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	0.70%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Credit Impaired Acquired Loans [Member] | Commercial & Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	3,255us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	3,476us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember
Credit Impaired Acquired Loans [Member] | HELOC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	9,202us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	10,139us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember
Ratio of type of loan to total loans receivable	0.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	0.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember
Credit Impaired Acquired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	$ 54us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	$ 55us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember

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A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

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Amount of deferred interest and fee income, unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of acquired loans. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

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-Publisher FASB

-Name Accounting Standards Codification

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

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-Section 45

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+ References

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+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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