Loans Receivable And Allowance For Credit Losses (Summary Of Loan Portfolio Segment Disaggregated By The Company's Impairment Method) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Financing Receivable, Impaired [Line Items]
Recorded investment in loans collectively evaluated for impairment	$ 7,414,539	$ 7,404,179
Recorded investment in loans individually evaluated for impairment	24,103	21,794
Financing receivable, total recorded investment	7,438,642	7,425,973
ACL for loans collectively evaluated for impairment	9,210	9,226
ACL for loans individually evaluated for impairment	225	0
One- to Four-Family Segment [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment in loans collectively evaluated for impairment	6,543,382	6,509,292
Recorded investment in loans individually evaluated for impairment	21,344	21,389
Financing receivable, total recorded investment	6,564,726	6,530,681
ACL for loans collectively evaluated for impairment	3,859	3,890
ACL for loans individually evaluated for impairment	0	0
One- to Four-Family Segment [Member] \| Originated [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment in loans collectively evaluated for impairment	3,936,436	3,881,100
Recorded investment in loans individually evaluated for impairment	14,568	14,683
Financing receivable, total recorded investment	3,951,004	3,895,783
ACL for loans collectively evaluated for impairment	2,047	2,000
ACL for loans individually evaluated for impairment	0	0
One- to Four-Family Segment [Member] \| Correspondent Purchased [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment in loans collectively evaluated for impairment	2,373,197	2,379,651
Recorded investment in loans individually evaluated for impairment	1,756	1,763
Financing receivable, total recorded investment	2,374,953	2,381,414
ACL for loans collectively evaluated for impairment	1,200	1,203
ACL for loans individually evaluated for impairment	0	0
One- to Four-Family Segment [Member] \| Bulk Purchased [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment in loans collectively evaluated for impairment	233,749	248,541
Recorded investment in loans individually evaluated for impairment	5,020	4,943
Financing receivable, total recorded investment	238,769	253,484
ACL for loans collectively evaluated for impairment	612	687
ACL for loans individually evaluated for impairment	0	0
Commercial Segment [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment in loans collectively evaluated for impairment	742,242	763,662
Recorded investment in loans individually evaluated for impairment	2,432	60
Financing receivable, total recorded investment	744,674	763,722
ACL for loans collectively evaluated for impairment	5,193	5,171
ACL for loans individually evaluated for impairment	225	0
Consumer Segment [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment in loans collectively evaluated for impairment	128,915	131,225
Recorded investment in loans individually evaluated for impairment	327	345
Financing receivable, total recorded investment	129,242	131,570
ACL for loans collectively evaluated for impairment	158	165
ACL for loans individually evaluated for impairment	$ 0	$ 0

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
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The balance of financing receivables that were individually evaluated for impairment.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
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-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

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

+ References

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 http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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