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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
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Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | $ 9,014,755 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount |  | $ 8,669,717 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount |  |  |
Ratio of type of loan to total loans receivable | 100.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans |  | 100.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans |  |  |
Allowance for probable losses | 108,323 us-gaap_FinancingReceivableAllowanceForCreditLosses | 108,700 us-gaap_FinancingReceivableAllowanceForCreditLosses | 112,347 us-gaap_FinancingReceivableAllowanceForCreditLosses | 114,931 us-gaap_FinancingReceivableAllowanceForCreditLosses | 118,158 us-gaap_FinancingReceivableAllowanceForCreditLosses | 116,741 us-gaap_FinancingReceivableAllowanceForCreditLosses
Loans in process | 426,836 us-gaap_LoansAndLeasesReceivableLoansInProcess |  | 346,172 us-gaap_LoansAndLeasesReceivableLoansInProcess |  |  |
Discount on acquired loans | 20,845 wfsl_DiscountOnAcquiredLoans |  | 25,391 wfsl_DiscountOnAcquiredLoans |  |  |
Deferred net origination fees | 37,763 us-gaap_LoansAndLeasesReceivableDeferredIncome |  | 37,485 us-gaap_LoansAndLeasesReceivableDeferredIncome |  |  |
Charges against loans receivable | 593,767 wfsl_LoansAndLeasesReceivableChargesToAllowanceLoansInProcessAndDeferredFees |  | 521,395 wfsl_LoansAndLeasesReceivableChargesToAllowanceLoansInProcessAndDeferredFees |  |  |
Loans receivable, net | 8,420,988 us-gaap_LoansAndLeasesReceivableNetReportedAmount |  | 8,148,322 us-gaap_LoansAndLeasesReceivableNetReportedAmount |  |  |
Single-Family Residential [Member] |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | 5,546,403 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  | 5,572,244 us-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 | 54,762 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 55,495 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 62,763 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 63,348 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 67,692 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 64,184 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Construction - Speculative [Member] |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | 163,657 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember |  | 140,060 us-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 | 5,445 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember | 5,451 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember | 6,742 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember | 6,773 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember | 8,142 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember | 8,407 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember
Construction - Custom [Member] |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | 370,693 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember |  | 385,824 us-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 | 968 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember | 965 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember | 1,695 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember | 1,599 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember | 1,474 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember | 882 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember
Land - Acquisition & Development [Member] |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | 107,181 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember |  | 80,359 us-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 | 7,405 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember | 6,671 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember | 5,592 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember | 6,027 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember | 7,084 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember | 9,165 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember
Land - Consumer Lot Loans [Member] |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | 104,558 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember |  | 111,130 us-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 | 3,035 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember | 3,113 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember | 3,077 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember | 2,974 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember | 3,274 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember | 3,552 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember
Multi-Family [Member] |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | 1,012,915 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember |  | 920,285 us-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 | 4,673 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember | 4,500 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember | 4,248 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember | 4,187 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember | 4,109 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember | 3,816 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember
Commercial Real Estate [Member] |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | 885,177 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  | 752,957 us-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 | 6,734 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 5,872 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 7,548 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 5,924 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 5,868 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 5,595 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial & Industrial [Member] |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | 466,207 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember |  | 434,088 us-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 | 21,146 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember | 23,328 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember | 16,527 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember | 20,403 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember | 16,505 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember | 16,614 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember
HELOC [Member] |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | 136,439 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember |  | 134,455 us-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 | 850 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember | 892 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember | 928 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember | 975 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember | 943 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember | 1,002 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember
Consumer [Member] |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | 221,525 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  | 138,315 us-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 | 3,305 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 2,413 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 3,227 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 2,721 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 3,067 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 3,524 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Non-Acquired Loans [Member] |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | 8,775,673 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember |  | 8,409,022 us-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 | 5,535,104 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  | 5,560,203 us-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 | 163,657 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember |  | 140,060 us-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 | 370,693 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember |  | 385,824 us-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 | 105,058 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember |  | 77,832 us-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 | 102,082 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember |  | 108,623 us-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 | 1,010,003 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember |  | 917,286 us-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 | 741,137 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  | 591,336 us-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 | 408,358 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember |  | 379,226 us-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 | 120,901 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember |  | 116,042 us-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 | 218,680 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_NonAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  | 132,590 us-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 | 169,559 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember |  | 181,355 us-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 | 10,977 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  | 11,716 us-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 | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember |  | 0 us-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 | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionCustomMember |  | 0 us-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 | 728 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember |  | 905 us-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 | 2,476 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandConsumerLotLoansMember |  | 2,507 us-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 | 2,912 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember |  | 2,999 us-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 | 87,313 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  | 97,898 us-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 | 55,659 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember |  | 51,386 us-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 | 6,700 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember |  | 8,274 us-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 | 2,794 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_AcquiredNonImpairedLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  | 5,670 us-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 | 69,523 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember |  | 79,340 us-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 | 322 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  | 325 us-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 | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_ConstructionSpeculativeMember |  | 0 us-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 |  |  |
Credit Impaired Acquired Loans [Member] | Land - Acquisition & Development [Member] |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans receivable, gross | 1,395 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_LandAcquisitionAndDevelopmentMember |  | 1,622 us-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 | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember |  | 0 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember |  |  |
Ratio of type of loan to total loans receivable | 0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_MultiFamilyHousingPortfolioSegmentMember |  | 0.00%wfsl_LoansAndLeasesReceivableRatioOfLoanTypeToAllLoans / 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 | 56,727 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  | 63,723 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |  |
Ratio of type of loan to total loans receivable | 0.60%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 | 2,190 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_CommercialAndIndustrialLoansMember |  | 3,476 us-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 | 8,838 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = wfsl_HomeEquityLineOfCreditMember |  | 10,139 us-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 | $ 51 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_BusinessAcquisitionAxis = wfsl_CreditImpairedAcquiredLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  | $ 55 us-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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