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Fair Value Measurements - Measured on a Recurring and Nonrecurring Basis (Details) (USD $)	3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	$ 2,895,056,000us-gaap_AvailableForSaleSecurities		$ 3,049,442,000us-gaap_AvailableForSaleSecurities
Liabilities, recurring	0us-gaap_LiabilitiesFairValueDisclosureRecurring	0us-gaap_LiabilitiesFairValueDisclosureRecurring
Liabilities, nonrecurring	0us-gaap_LiabilitiesFairValueDisclosureNonrecurring	0us-gaap_LiabilitiesFairValueDisclosureNonrecurring
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	2,895,056,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember		3,049,442,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Level 1 to level 2 transfers	0us-gaap_FairValueAssetsLevel1ToLevel2TransfersAmount / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember		0us-gaap_FairValueAssetsLevel1ToLevel2TransfersAmount / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Level 2 to level 1 transfers	0us-gaap_FairValueAssetsLevel2ToLevel1TransfersAmount / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember		0us-gaap_FairValueAssetsLevel2ToLevel1TransfersAmount / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Level 1 to level 3 transfers	0wfsl_FairValueAssetsLevel1toLevel3TransfersAmount / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember		0wfsl_FairValueAssetsLevel1toLevel3TransfersAmount / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Level 3 to level 1 transfers	0wfsl_FairValueAssetsLevel3toLevel1TransfersAmount / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember		0wfsl_FairValueAssetsLevel3toLevel1TransfersAmount / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Level 2 to level 3 transfers	0wfsl_FairValueAssetsLevel2toLevel3TransfersAmount / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember		0wfsl_FairValueAssetsLevel2toLevel3TransfersAmount / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Level 3 to level 2 transfers	0wfsl_FairValueAssetsLevel3toLevel2TransfersAmount / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember		0wfsl_FairValueAssetsLevel3toLevel2TransfersAmount / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	101,636,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember		101,387,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	2,793,420,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember		2,948,055,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	0us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember		0us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	38,088,000us-gaap_AssetsFairValueDisclosureNonrecurring / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	17,208,000us-gaap_AssetsFairValueDisclosureNonrecurring / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	146,000us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_ImpairedLoansMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	5,580,000us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_ImpairedLoansMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Covered Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	1,041,000us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_CoveredRealEstateOwnedMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	1,286,000us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_CoveredRealEstateOwnedMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Real Estate Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	36,901,000us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_RealEstateHeldForSaleMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	10,342,000us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_RealEstateHeldForSaleMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Change During Period, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Losses (gains), nonrecurring	(8,173,000)wfsl_LossRelatedToImpairedLoansAndRealEstateHeldForSaleMeasuredOnNonrecurringBasis / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_ChangeDuringPeriodFairValueDisclosureMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	2,985,000wfsl_LossRelatedToImpairedLoansAndRealEstateHeldForSaleMeasuredOnNonrecurringBasis / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_ChangeDuringPeriodFairValueDisclosureMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Change During Period, Fair Value Disclosure [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Losses (gains), nonrecurring	64,000wfsl_LossRelatedToImpairedLoansAndRealEstateHeldForSaleMeasuredOnNonrecurringBasis / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_ImpairedLoansMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_ChangeDuringPeriodFairValueDisclosureMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	(805,000)wfsl_LossRelatedToImpairedLoansAndRealEstateHeldForSaleMeasuredOnNonrecurringBasis / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_ImpairedLoansMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_ChangeDuringPeriodFairValueDisclosureMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Change During Period, Fair Value Disclosure [Member] | Covered Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Losses (gains), nonrecurring	75,000wfsl_LossRelatedToImpairedLoansAndRealEstateHeldForSaleMeasuredOnNonrecurringBasis / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_CoveredRealEstateOwnedMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_ChangeDuringPeriodFairValueDisclosureMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	65,000wfsl_LossRelatedToImpairedLoansAndRealEstateHeldForSaleMeasuredOnNonrecurringBasis / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_CoveredRealEstateOwnedMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_ChangeDuringPeriodFairValueDisclosureMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Change During Period, Fair Value Disclosure [Member] | Real Estate Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Losses (gains), nonrecurring	(8,312,000)wfsl_LossRelatedToImpairedLoansAndRealEstateHeldForSaleMeasuredOnNonrecurringBasis / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_RealEstateHeldForSaleMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_ChangeDuringPeriodFairValueDisclosureMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	3,725,000wfsl_LossRelatedToImpairedLoansAndRealEstateHeldForSaleMeasuredOnNonrecurringBasis / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_RealEstateHeldForSaleMember / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_ChangeDuringPeriodFairValueDisclosureMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0us-gaap_AssetsFairValueDisclosureNonrecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	0us-gaap_AssetsFairValueDisclosureNonrecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Level 1 [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_ImpairedLoansMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	0us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_ImpairedLoansMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Level 1 [Member] | Covered Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_CoveredRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	0us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_CoveredRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Level 1 [Member] | Real Estate Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_RealEstateHeldForSaleMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	0us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_RealEstateHeldForSaleMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0us-gaap_AssetsFairValueDisclosureNonrecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	0us-gaap_AssetsFairValueDisclosureNonrecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_ImpairedLoansMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	0us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_ImpairedLoansMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member] | Covered Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_CoveredRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	0us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_CoveredRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member] | Real Estate Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_RealEstateHeldForSaleMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	0us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_RealEstateHeldForSaleMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	38,088,000us-gaap_AssetsFairValueDisclosureNonrecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	17,208,000us-gaap_AssetsFairValueDisclosureNonrecurring / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	146,000us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_ImpairedLoansMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	5,580,000us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_ImpairedLoansMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Covered Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	1,041,000us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_CoveredRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	1,286,000us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_CoveredRealEstateOwnedMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Real Estate Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	36,901,000us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_RealEstateHeldForSaleMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember	10,342,000us-gaap_AssetsFairValueDisclosureNonrecurring / wfsl_AssetsMeasuredOnNonrecurringBasisByTypeAxis = wfsl_RealEstateHeldForSaleMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember
Equity Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	101,636,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember		101,387,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	101,636,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember		101,387,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	101,636,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember		101,387,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	0us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember		0us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	0us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember		0us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember
US Treasury and Government [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	620,018,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember		731,943,000us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember
US Treasury and Government [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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Obligations of States and Political Subdivisions [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ References

No definition available.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

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Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

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- Definition

Fair value adjustments to collateral dependent loans and real estate held for sale are recorded to reflect write-downs of principal balances based on the current appraised or estimated value of the collateral.

+ References

No definition available.

+ Details

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- Details

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