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Loans Receivable (excluding Covered Loans) - Schedule of Accounts, Notes, Loans, and Financing Receivable (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	$ 9,014,755us-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	108,323us-gaap_FinancingReceivableAllowanceForCreditLosses	108,700us-gaap_FinancingReceivableAllowanceForCreditLosses	112,347us-gaap_FinancingReceivableAllowanceForCreditLosses	114,931us-gaap_FinancingReceivableAllowanceForCreditLosses	118,158us-gaap_FinancingReceivableAllowanceForCreditLosses	116,741us-gaap_FinancingReceivableAllowanceForCreditLosses
Loans in process	426,836us-gaap_LoansAndLeasesReceivableLoansInProcess		346,172us-gaap_LoansAndLeasesReceivableLoansInProcess
Discount on acquired loans	20,845wfsl_DiscountOnAcquiredLoans		25,391wfsl_DiscountOnAcquiredLoans
Deferred net origination fees	37,763us-gaap_LoansAndLeasesReceivableDeferredIncome		37,485us-gaap_LoansAndLeasesReceivableDeferredIncome
Charges against loans receivable	593,767wfsl_LoansAndLeasesReceivableChargesToAllowanceLoansInProcessAndDeferredFees		521,395wfsl_LoansAndLeasesReceivableChargesToAllowanceLoansInProcessAndDeferredFees
Loans receivable, net	8,420,988us-gaap_LoansAndLeasesReceivableNetReportedAmount		8,148,322us-gaap_LoansAndLeasesReceivableNetReportedAmount
Single-Family Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	5,546,403us-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	61.50%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember		64.20%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Allowance for probable losses	54,762us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	55,495us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	62,763us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	63,348us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	67,692us-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	163,657us-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	1.80%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember		1.60%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember
Allowance for probable losses	5,445us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember	5,451us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember	6,742us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember	6,773us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember	8,142us-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	370,693us-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	4.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember		4.50%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember
Allowance for probable losses	968us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember	965us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember	1,695us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember	1,599us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember	1,474us-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	107,181us-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	1.20%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember		0.90%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Allowance for probable losses	7,405us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	6,671us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	5,592us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	6,027us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember	7,084us-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	104,558us-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	3,035us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember	3,113us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember	3,077us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember	2,974us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember	3,274us-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	1,012,915us-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	4,673us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	4,500us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	4,248us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	4,187us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember	4,109us-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	885,177us-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	9.80%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember		8.70%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Allowance for probable losses	6,734us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	5,872us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	7,548us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	5,924us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	5,868us-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	466,207us-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	21,146us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	23,328us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	16,527us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	20,403us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember	16,505us-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	136,439us-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	850us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	892us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	928us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	975us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember	943us-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	221,525us-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	2.50%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember		1.60%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Allowance for probable losses	3,305us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	2,413us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	3,227us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	2,721us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	3,067us-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	8,775,673us-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	97.50%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	5,535,104us-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	61.40%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	163,657us-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	1.80%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	370,693us-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	4.10%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	105,058us-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	1.20%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	102,082us-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	1,010,003us-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	741,137us-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	8.20%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	408,358us-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	4.60%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	120,901us-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	218,680us-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	2.50%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 Non-Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	169,559us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember		181,355us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember
Ratio of type of loan to total loans receivable	1.80%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember		2.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember
Acquired Non-Impaired Loans [Member] | Single-Family Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	10,977us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember		11,716us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Ratio of type of loan to total loans receivable	0.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember		0.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Acquired Non-Impaired Loans [Member] | Construction - Speculative [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember		0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember		0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember
Acquired Non-Impaired Loans [Member] | Construction - Custom [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember		0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember		0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember
Acquired Non-Impaired Loans [Member] | Land - Acquisition & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	728us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember		905us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember		0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Acquired Non-Impaired Loans [Member] | Land - Consumer Lot Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	2,476us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember		2,507us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember		0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember
Acquired Non-Impaired Loans [Member] | Multi-Family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	2,912us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember		2,999us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember		0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember
Acquired Non-Impaired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	87,313us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember		97,898us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Ratio of type of loan to total loans receivable	1.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember		1.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Acquired Non-Impaired Loans [Member] | Commercial & Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	55,659us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember		51,386us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember
Ratio of type of loan to total loans receivable	0.60%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember		0.60%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember
Acquired Non-Impaired Loans [Member] | HELOC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	6,700us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember		8,274us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember
Ratio of type of loan to total loans receivable	0.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember		0.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember
Acquired Non-Impaired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	2,794us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember		5,670us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember		0.10%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Credit Impaired Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	69,523us-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	0.70%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	322us-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] | Construction - Speculative [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember		0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember
Ratio of type of loan to total loans receivable	0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember		0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember
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