Allowance for Losses on Loans - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	$ 108,323	$ 114,931	$ 112,347	$ 116,741
FinancingReceivableAllowanceForCreditLossesWriteOffs	6,551	3,400	11,677	12,986
Recoveries	6,238	5,619	15,329	22,745
Provision & Transfers	(2,399)	(3,000)	(10,388)	(12,350)
Ending Allowance	105,611	114,150	105,611	114,150
Single-Family Residential [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	54,762	63,348	62,763	64,184
FinancingReceivableAllowanceForCreditLossesWriteOffs	1,698	2,530	4,801	7,307
Recoveries	3,878	4,717	10,553	15,631
Provision & Transfers	(4,938)	(3,175)	(16,511)	(10,148)
Ending Allowance	52,004	62,360	52,004	62,360
Construction - Speculative [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	5,445	6,773	6,742	8,407
FinancingReceivableAllowanceForCreditLossesWriteOffs	0	0	388	938
Recoveries	0	2	75	97
Provision & Transfers	488	(388)	(496)	(1,179)
Ending Allowance	5,933	6,387	5,933	6,387
Construction - Custom [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	968	1,599	1,695	882
FinancingReceivableAllowanceForCreditLossesWriteOffs	0	0	0	0
Recoveries	0	0	0	0
Provision & Transfers	17	79	(710)	796
Ending Allowance	985	1,678	985	1,678
Land - Acquisition & Development [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	7,405	6,027	5,592	9,165
FinancingReceivableAllowanceForCreditLossesWriteOffs	0	0	38	541
Recoveries	1	85	206	823
Provision & Transfers	(1,634)	843	12	(2,492)
Ending Allowance	5,772	6,955	5,772	6,955
Land - Consumer Lot Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	3,035	2,974	3,077	3,552
FinancingReceivableAllowanceForCreditLossesWriteOffs	276	86	363	559
Recoveries	187	0	221	22
Provision & Transfers	53	(26)	64	(153)
Ending Allowance	2,999	2,862	2,999	2,862
Multi-Family [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	4,673	4,187	4,248	3,816
FinancingReceivableAllowanceForCreditLossesWriteOffs	0	0	0	0
Recoveries	0	0	220	0
Provision & Transfers	362	(46)	567	325
Ending Allowance	5,035	4,141	5,035	4,141
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	6,734	5,924	7,548	5,595
FinancingReceivableAllowanceForCreditLossesWriteOffs	1,592	32	1,619	105
Recoveries	230	24	711	24
Provision & Transfers	1,896	773	628	1,175
Ending Allowance	7,268	6,689	7,268	6,689
Commercial & Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	21,146	20,403	16,527	16,614
FinancingReceivableAllowanceForCreditLossesWriteOffs	2,106	38	2,461	730
Recoveries	896	4	948	3,277
Provision & Transfers	1,726	(1,673)	6,648	(465)
Ending Allowance	21,662	18,696	21,662	18,696
HELOC [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	850	975	928	1,002
FinancingReceivableAllowanceForCreditLossesWriteOffs	26	18	26	18
Recoveries	1	0	1	0
Provision & Transfers	39	58	(39)	31
Ending Allowance	864	1,015	864	1,015
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	3,305	2,721	3,227	3,524
FinancingReceivableAllowanceForCreditLossesWriteOffs	853	696	1,981	2,788
Recoveries	1,045	787	2,394	2,871
Provision & Transfers	(408)	555	(551)	(240)
Ending Allowance	$ 3,089	$ 3,367	$ 3,089	$ 3,367

A valuation allowance for financing receivables that are expected to be uncollectible.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

+ Details

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

- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(4)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Amount of direct write-downs of financing receivables charged against the allowance.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Financing Receivable, Allowance for Credit Losses, Provision and Transfers

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=wfsl_ConstructionSpeculativeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=wfsl_ConstructionCustomMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=wfsl_LandAcquisitionAndDevelopmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=wfsl_LandConsumerLotLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=wfsl_MultiFamilyHousingPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=wfsl_CommercialAndIndustrialLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=wfsl_HomeEquityLineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: