Loans Receivable (excluding Covered Loans) - Schedule of Changes in the Accretable Yield for Acquired Loans (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
Mar. 31, 2015	Sep. 30, 2014
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Accretion, carrying amount of loans	$ 284	$ 802
Credit Impaired Acquired Loans [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period, accretable yield	32,591	37,236
Balance at beginning of period, carrying amount of loans	57,771	69,718
Reclassification from nonaccretable balance, net, accretable yield		7,300
Reclassification from nonaccretable balance, net, carrying value of loans		0
Additions, accretable yield	0
Additions, carrying amount of loans	0
Accretion, accretable yield	(6,036)	(11,945)
Accretion, carrying amount of loans	6,036	11,945
Transfers to REO, accretable yield	0	0
Transfers to REO, carrying amount of loans	0	(1,188)
Payments received, net, accretable yield	0	0
Payments received, net, carrying amount of loans	(12,362)	(22,704)
Balance at end of period, accretable yield	26,555	32,591
Balance at end of period, carrying amount of loans	51,445	57,771
Acquired Non-Impaired Loans [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period, accretable yield	4,254	4,977
Balance at beginning of period, carrying amount of loans	177,440	245,373
Reclassification from nonaccretable balance, net, accretable yield		0
Reclassification from nonaccretable balance, net, carrying value of loans		0
Additions, accretable yield	346
Additions, carrying amount of loans	0
Accretion, accretable yield	(1,810)	(723)
Accretion, carrying amount of loans	1,810	723
Transfers to REO, accretable yield	0	0
Transfers to REO, carrying amount of loans	0	(4,710)
Payments received, net, accretable yield	0	0
Payments received, net, carrying amount of loans	(12,516)	(63,946)
Balance at end of period, accretable yield	2,790	4,254
Balance at end of period, carrying amount of loans	$ 166,734	$ 177,440

Amount of the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 15

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=27045933&loc=d3e13503-111538

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

+ Details

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

- Definition

Amount of decrease from accretion of the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

+ References

+ Details

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

- Definition

Amount of additions to the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

+ References

+ Details

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

- Details

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

- Definition

Amount of increase of reclassification from nonaccretable difference to the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

+ References

+ Details

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

- Definition

The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 15

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=27045933&loc=d3e13503-111538

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

+ Details

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

- Definition

Certain Loans Acquired in Transfer not Accounted for as Debt Securities Accretable Yield, Payments

+ References

No definition available.

+ Details

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

- Definition

Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Transfers to Real Estate Owned

+ References

No definition available.

+ Details

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

- Definition

Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount of Loans, Additions

+ References

No definition available.

+ Details

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

- Definition

Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount of Loans, Reclassifications from Nonaccretable Difference

+ References

No definition available.

+ Details

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

- Definition

Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Payments

+ References

No definition available.

+ Details

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

- Definition

Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Transfers to Real Estate Owned

+ References

No definition available.

+ Details

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

- Definition

FDIC Indemnification Asset, Discount Accretion

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=wfsl_AcquiredNonImpairedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=wfsl_CreditImpairedAcquiredLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: