Loans Receivable And Allowance For Credit Losses (Loans, Past Due Aging Analysis) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Sep. 30, 2021
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	$ 7,252,479	$ 7,100,965
Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	19,698	19,515
Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	11,243	7,861
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	8,455	11,654
Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	7,232,781	7,081,450
One- to Four-Family Segment [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	6,255,850	6,180,495
One- to Four-Family Segment [Member] | Originated [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	4,007,912	3,979,536
One- to Four-Family Segment [Member] | Originated [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	8,602	7,819
One- to Four-Family Segment [Member] | Originated [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	6,021	4,142
One- to Four-Family Segment [Member] | Originated [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	2,581	3,677
One- to Four-Family Segment [Member] | Originated [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	3,999,310	3,971,717
One- to Four-Family Segment [Member] | Correspondent Purchased [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	2,095,922	2,026,592
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	6,208	5,886
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	3,513	2,629
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	2,695	3,257
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	2,089,714	2,020,706
One- to Four-Family Segment [Member] | Bulk Purchased [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	152,016	174,367
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	2,572	3,558
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	755	555
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	1,817	3,003
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	149,444	170,809
Commercial Segment [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	900,928	826,007
Commercial Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	829,968	759,629
Commercial Segment [Member] | Commercial Real Estate [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	1,750	1,121
Commercial Segment [Member] | Commercial Real Estate [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	675	37
Commercial Segment [Member] | Commercial Real Estate [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	1,075	1,084
Commercial Segment [Member] | Commercial Real Estate [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	828,218	758,508
Commercial Segment [Member] | Commercial and Industrial [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	70,960	66,378
Commercial Segment [Member] | Commercial and Industrial [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	136	135
Commercial Segment [Member] | Commercial and Industrial [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	23	0
Commercial Segment [Member] | Commercial and Industrial [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	113	135
Commercial Segment [Member] | Commercial and Industrial [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	70,824	66,243
Consumer Segment [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	95,701	94,463
Consumer Segment [Member] | Home Equity [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	87,414	86,385
Consumer Segment [Member] | Home Equity [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	404	981
Consumer Segment [Member] | Home Equity [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	230	496
Consumer Segment [Member] | Home Equity [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	174	485
Consumer Segment [Member] | Home Equity [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	87,010	85,404
Consumer Segment [Member] | Other [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	8,287	8,078
Consumer Segment [Member] | Other [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	26	15
Consumer Segment [Member] | Other [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	26	2
Consumer Segment [Member] | Other [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	0	13
Consumer Segment [Member] | Other [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	$ 8,261	$ 8,063