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

Amount of loan with fixed rate of interest.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522

Name:	us-gaap_LoansReceivableWithFixedRatesOfInterest1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of loan with variable or adjustable rate of interest.

Name:	us-gaap_LoansReceivableWithVariableRatesOfInterest1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Financing Receivable with Fixed Rates of Interest, Percent of Gross

No definition available.

Name:	wfsl_FinancingReceivableWithFixedRatesOfInterestPercentOfGross
Namespace Prefix:	wfsl_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

Financing Receivable with Variable Rates of Interest, Percent of Gross

No definition available.

Name:	wfsl_FinancingReceivableWithVariableRatesOfInterestPercentOfGross
Namespace Prefix:	wfsl_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

Name:	wfsl_FinancingReceivableInterestRateTypeByTermToMaturityAxis=wfsl_WithinOneYearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	wfsl_FinancingReceivableInterestRateTypeByTermToMaturityAxis=wfsl_MoreThanOneWithinThreeYearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	wfsl_FinancingReceivableInterestRateTypeByTermToMaturityAxis=wfsl_MoreThanThreeWithinFiveYearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	wfsl_FinancingReceivableInterestRateTypeByTermToMaturityAxis=wfsl_MoreThanFiveWithinTenYearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	wfsl_FinancingReceivableInterestRateTypeByTermToMaturityAxis=wfsl_MoreThanTenWithinTwentyYearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: