XML 19 R42.htm IDEA: XBRL DOCUMENT v2.4.1.9
Fair Value Measurements - Investments by Contractual Maturity Date (Details) (USD $)
 3 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Sep. 30, 2014
Amortized Cost, Available-for-sale securities      
Amortized Cost $ 2,853,487,000us-gaap_AvailableForSaleSecuritiesAmortizedCost   $ 3,016,432,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
Gross Unrealized Gains / Losses, Available-for-sale securities      
Gross unrealized gains 45,420,000wfsl_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments   37,273,000wfsl_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments
Gross unrealized loss (3,851,000)wfsl_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments   (4,263,000)wfsl_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments
Fair Value, Available-for-sale securities      
Fair Value 2,895,056,000us-gaap_AvailableForSaleSecurities   3,049,442,000us-gaap_AvailableForSaleSecurities
Yield, Available-for-sale securities      
Yield 1.99%wfsl_AvailableForSaleSecuritiesYield   1.99%wfsl_AvailableForSaleSecuritiesYield
Yield, Held-to-maturity securities      
Investments 4,369,706,000us-gaap_Investments   4,564,697,000us-gaap_Investments
Gross unrealized gains on investments 54,504,000wfsl_GrossUnrealizedGainsOnInvestments   42,128,000wfsl_GrossUnrealizedGainsOnInvestments
Gross unrealized losses on investments (25,373,000)wfsl_GrossUnrealizedLossesOnInvestments   (58,165,000)wfsl_GrossUnrealizedLossesOnInvestments
Fair value of investments 4,398,837,000us-gaap_InvestmentsFairValueDisclosure   4,548,660,000us-gaap_InvestmentsFairValueDisclosure
Yield on investments 2.39%wfsl_Yield   2.38%wfsl_Yield
Available-for-sale securities sold 0us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities 0us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities  
Term of contractual due dates of substantially all mortgage-backed securities 10 years    
US Treasury and Government [Member]      
Amortized Cost, Available-for-sale securities      
1 to 5 years 120,467,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   171,154,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
5 to 10 years 153,525,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   203,317,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Over 10 years 344,088,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   354,828,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Gross Unrealized Gains / Losses, Available-for-sale securities      
Gross unrealized gains, 1 to 5 years 2,396,000wfsl_GrossUnrealizedGainsAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   2,585,000wfsl_GrossUnrealizedGainsAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Gross unrealized gains, 5 to 10 years 64,000wfsl_GrossUnrealizedGainsAfterFiveThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   300,000wfsl_GrossUnrealizedGainsAfterFiveThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Gross unrealized gains, Over 10 years 336,000wfsl_GrossUnrealizedGainsAfterTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   1,028,000wfsl_GrossUnrealizedGainsAfterTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Gross unrealized losses, 1 to 5 years (426,000)wfsl_GrossUnrealizedLossesAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   (748,000)wfsl_GrossUnrealizedLossesAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Gross unrealized losses, 5 to 10 years (5,000)wfsl_GrossUnrealizedLossesAfterFiveYearsThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   (102,000)wfsl_GrossUnrealizedLossesAfterFiveYearsThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Gross unrealized losses, Over 10 years (427,000)wfsl_GrossUnrealizedLossesOverTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   (419,000)wfsl_GrossUnrealizedLossesOverTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Fair Value, Available-for-sale securities      
1 to 5 years 122,437,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   172,991,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
5 to 10 years 153,584,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   203,515,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Over 10 years 343,997,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   355,437,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Yield, Available-for-sale securities      
1 to 5 years 1.47%wfsl_AvailableforsaleSecuritiesYieldAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   1.26%wfsl_AvailableforsaleSecuritiesYieldAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
5 to 10 years 1.12%wfsl_AvailableforsaleSecuritiesYieldAfterFiveThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   1.45%wfsl_AvailableforsaleSecuritiesYieldAfterFiveThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Over 10 years 1.26%wfsl_AvailableforsaleSecuritiesYieldAfterTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		   1.25%wfsl_AvailableforsaleSecuritiesYieldAfterTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Equity Securities [Member]      
Amortized Cost, Available-for-sale securities      
Within 1 year 500,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		    
1 to 5 years 100,000,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		   100,500,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
5 to 10 years 0us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		   0us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Gross Unrealized Gains / Losses, Available-for-sale securities      
Gross unrealized gains, Within 1 year 16,000wfsl_GrossUnrealizedGainsWithinOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		    
Gross unrealized gains, 1 to 5 years 1,120,000wfsl_GrossUnrealizedGainsAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		   887,000wfsl_GrossUnrealizedGainsAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Gross unrealized gains, 5 to 10 years 0wfsl_GrossUnrealizedGainsAfterFiveThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		   0wfsl_GrossUnrealizedGainsAfterFiveThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Gross unrealized losses, Within 1 year 0wfsl_GrossUnrealizedLossesWithinOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		    
Gross unrealized losses, 1 to 5 years 0wfsl_GrossUnrealizedLossesAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		   0wfsl_GrossUnrealizedLossesAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Gross unrealized losses, 5 to 10 years 0wfsl_GrossUnrealizedLossesAfterFiveYearsThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		   0wfsl_GrossUnrealizedLossesAfterFiveYearsThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Fair Value, Available-for-sale securities      
Within 1 year 516,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		    
1 to 5 years 101,120,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		   101,387,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
5 to 10 years 0us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		   0us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Yield, Available-for-sale securities      
Within 1 year 1.80%wfsl_AvailableforsaleSecuritiesYieldWithinOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		    
1 to 5 years 1.90%wfsl_AvailableforsaleSecuritiesYieldAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		   1.90%wfsl_AvailableforsaleSecuritiesYieldAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
5 to 10 years 0.00%wfsl_AvailableforsaleSecuritiesYieldAfterFiveThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		   0.00%wfsl_AvailableforsaleSecuritiesYieldAfterFiveThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Corporate Debt Securities [Member]      
Amortized Cost, Available-for-sale securities      
Within 1 year 15,000,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   15,000,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
1 to 5 years 302,627,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   302,540,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
5 to 10 years 158,236,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   138,201,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Over 10 years 50,000,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   50,000,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Gross Unrealized Gains / Losses, Available-for-sale securities      
Gross unrealized gains, Within 1 year 67,000wfsl_GrossUnrealizedGainsWithinOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   75,000wfsl_GrossUnrealizedGainsWithinOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Gross unrealized gains, 1 to 5 years 1,524,000wfsl_GrossUnrealizedGainsAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   2,372,000wfsl_GrossUnrealizedGainsAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Gross unrealized gains, 5 to 10 years 1,787,000wfsl_GrossUnrealizedGainsAfterFiveThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   1,789,000wfsl_GrossUnrealizedGainsAfterFiveThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Gross unrealized gains, Over 10 years 0wfsl_GrossUnrealizedGainsAfterTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   0wfsl_GrossUnrealizedGainsAfterTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Gross unrealized losses, Within 1 year 0wfsl_GrossUnrealizedLossesWithinOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   0wfsl_GrossUnrealizedLossesWithinOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Gross unrealized losses, 1 to 5 years (6,000)wfsl_GrossUnrealizedLossesAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   0wfsl_GrossUnrealizedLossesAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Gross unrealized losses, 5 to 10 years (1,297,000)wfsl_GrossUnrealizedLossesAfterFiveYearsThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   (970,000)wfsl_GrossUnrealizedLossesAfterFiveYearsThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Gross unrealized losses, Over 10 years 0wfsl_GrossUnrealizedLossesOverTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   0wfsl_GrossUnrealizedLossesOverTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Fair Value, Available-for-sale securities      
Within 1 year 15,067,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   15,075,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
1 to 5 years 304,145,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   304,912,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
5 to 10 years 158,726,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   139,020,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Over 10 years 50,000,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   50,000,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Yield, Available-for-sale securities      
Within 1 year 1.00%wfsl_AvailableforsaleSecuritiesYieldWithinOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   1.00%wfsl_AvailableforsaleSecuritiesYieldWithinOneYear
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
1 to 5 years 0.71%wfsl_AvailableforsaleSecuritiesYieldAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   0.71%wfsl_AvailableforsaleSecuritiesYieldAfterOneThroughFiveYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
5 to 10 years 1.42%wfsl_AvailableforsaleSecuritiesYieldAfterFiveThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   1.43%wfsl_AvailableforsaleSecuritiesYieldAfterFiveThroughTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Over 10 years 3.00%wfsl_AvailableforsaleSecuritiesYieldAfterTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		   3.00%wfsl_AvailableforsaleSecuritiesYieldAfterTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Municipal Bonds [Member]      
Amortized Cost, Available-for-sale securities      
Over 10 years 20,397,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember		   20,402,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember
Gross Unrealized Gains / Losses, Available-for-sale securities      
Gross unrealized gains, Over 10 years 3,671,000wfsl_GrossUnrealizedGainsAfterTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember		   3,279,000wfsl_GrossUnrealizedGainsAfterTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember
Gross unrealized losses, Over 10 years 0wfsl_GrossUnrealizedLossesOverTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember		   0wfsl_GrossUnrealizedLossesOverTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember
Fair Value, Available-for-sale securities      
Over 10 years 24,068,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember		   23,681,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember
Yield, Available-for-sale securities      
Over 10 years 6.45%wfsl_AvailableforsaleSecuritiesYieldAfterTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember		   6.45%wfsl_AvailableforsaleSecuritiesYieldAfterTenYears
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MunicipalBondsMember
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]      
Amortized Cost, Available-for-sale securities      
Without single maturity date 1,495,114,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		   1,561,639,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Gross Unrealized Gains / Losses, Available-for-sale securities      
Gross unrealized gains, Without single maturity date 34,386,000wfsl_GrossUnrealizedGainsWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		   24,893,000wfsl_GrossUnrealizedGainsWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Gross unrealized losses, Without single maturity date (1,690,000)wfsl_GrossUnrealizedLossesWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		   (2,024,000)wfsl_GrossUnrealizedLossesWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Fair Value, Available-for-sale securities      
Without single maturity date 1,527,810,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		   1,584,508,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Yield, Available-for-sale securities      
Without single maturity date 2.57%wfsl_AvailableforsaleSecuritiesYieldWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		   2.57%wfsl_AvailableforsaleSecuritiesYieldWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Amortized Cost, Held-to-maturity securities      
Without single maturity date 1,516,219,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		   1,548,265,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Gross Unrealized Gains / Losses, Held-to-maturity securities      
Gross unrealized gains, Without single maturity date 9,084,000wfsl_GrossUnrecognizedGainsWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		   4,855,000wfsl_GrossUnrecognizedGainsWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Gross unrealized losses, Without single maturity date (21,522,000)wfsl_GrossUnrecognizedLossesWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		   (53,902,000)wfsl_GrossUnrecognizedLossesWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Fair Value, Held-to-maturity securities      
Without single maturity date 1,503,781,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		   1,499,218,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Yield, Held-to-maturity securities      
Without a single maturity date 3.13%wfsl_HeldtomaturitySecuritiesYieldWithoutASingleMaturityDate
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		   3.13%wfsl_HeldtomaturitySecuritiesYieldWithoutASingleMaturityDate
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Commercial Mortgage Backed Securities [Member]      
Amortized Cost, Available-for-sale securities      
Without single maturity date 93,533,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		   98,851,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Gross Unrealized Gains / Losses, Available-for-sale securities      
Gross unrealized gains, Without single maturity date 53,000wfsl_GrossUnrealizedGainsWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		   65,000wfsl_GrossUnrealizedGainsWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Gross unrealized losses, Without single maturity date 0wfsl_GrossUnrealizedLossesWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		   0wfsl_GrossUnrealizedLossesWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Fair Value, Available-for-sale securities      
Without single maturity date $ 93,586,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		   $ 98,916,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember
Yield, Available-for-sale securities      
Without single maturity date 1.51%wfsl_AvailableforsaleSecuritiesYieldWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		   1.49%wfsl_AvailableforsaleSecuritiesYieldWithoutSingleMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember