Name:	us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryByInterestRateTypeByMaturityAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of advance from Federal Home Loan Bank (FHLBank) maturing after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

Name:	us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueAfterFiveYearsOfBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of advance from Federal Home Loan Bank (FHLBank) maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Name:	us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueWithinOneYearOfBalanceSheetDate
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Federal Home Loan Bank, Advances, Maturities Summary, Due from One Year to Three Years of Balance Sheet Date

No definition available.

Name:	wfsl_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromOneYearToThreeYearsOfBalanceSheetDate
Namespace Prefix:	wfsl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Federal Home Loan Bank, Advances, Maturities Summary, Due from Three Years to Five Years of Balance Sheet Date

No definition available.