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

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the best estimate at the acquisition date of the contractual cash flows not expected to be collected, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4845-128472

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

Amount of decreases to the indemnification asset due to cash payments received relating to loss sharing agreements with the Federal Deposit Insurance Corporation (FDIC).

No definition available.

Name:	us-gaap_FDICIndemnificationAssetCashPaymentsReceived
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

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

Disclosure of the unamortized amount of the discount on the note or receivable which is deducted from the face amount of the receivable or loan. The discount or premium is the difference between the present value and the face amount.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 1A

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

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

FDIC Indemnification Asset, Additions (deletions)

No definition available.

Name:	wfsl_AdditionsdeletionstoFDICIndemnificationAsset
Namespace Prefix:	wfsl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

FDIC Indemnification Asset, Amortization

No definition available.

Name:	wfsl_FdicIndemnificationAssetAmortization
Namespace Prefix:	wfsl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

FDIC Indemnification Asset, Discount Accretion

No definition available.

Name:	wfsl_FdicIndemnificationAssetDiscountAccretion
Namespace Prefix:	wfsl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

FDIC Indemnification Asset Movement Analysis [Roll Forward]

No definition available.

Name:	wfsl_FdicIndemnificationAssetMovementAnalysisRollForward
Namespace Prefix:	wfsl_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The net present value of the amount expected to be received from the FDIC in connection with loss share agreements.

No definition available.