Loans Receivable And Allowance For Credit Losses (Loans, Past Due Aging Analysis) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Sep. 30, 2021
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	$ 7,113,140	$ 7,100,965
Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	23,459	19,515
Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	12,747	7,861
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	10,712	11,654
Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	7,089,681	7,081,450
One- to Four-Family Segment [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	6,154,444	6,180,495
One- to Four-Family Segment [Member] | Originated [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	3,973,279	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	10,927	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	6,993	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	3,934	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	3,962,352	3,971,717
One- to Four-Family Segment [Member] | Correspondent Purchased [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	2,015,169	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	8,371	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	5,213	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	3,158	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	2,006,798	2,020,706
One- to Four-Family Segment [Member] | Bulk Purchased [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	165,996	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	2,123	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	155	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	1,968	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	163,873	170,809
Commercial Segment [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	866,348	826,007
Commercial Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	790,084	759,629
Commercial Segment [Member] | Commercial Real Estate [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	1,273	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	222	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	1,051	1,084
Commercial Segment [Member] | Commercial Real Estate [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	788,811	758,508
Commercial Segment [Member] | Commercial and Industrial [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	76,264	66,378
Commercial Segment [Member] | Commercial and Industrial [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	124	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	0	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	124	135
Commercial Segment [Member] | Commercial and Industrial [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	76,140	66,243
Consumer Segment [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	92,348	94,463
Consumer Segment [Member] | Home Equity [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	84,528	86,385
Consumer Segment [Member] | Home Equity [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	615	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	149	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	466	485
Consumer Segment [Member] | Home Equity [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	83,913	85,404
Consumer Segment [Member] | Other [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	7,820	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	15	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	11	13
Consumer Segment [Member] | Other [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	$ 7,794	$ 8,063