Loans Receivable And Allowance For Credit Losses (Loans, Past Due Aging Analysis) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Sep. 30, 2022
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	$ 7,985,759	$ 7,480,579
Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	20,079	15,681
Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	14,195	6,506
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	5,884	9,175
Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	7,965,680	7,464,898
One- to Four-Family Segment [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	6,662,408	6,416,358
One- to Four-Family Segment [Member] | Originated [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	4,049,961	4,038,544
One- to Four-Family Segment [Member] | Originated [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	7,934	7,036
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	6,355	4,123
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	1,579	2,913
One- to Four-Family Segment [Member] | Originated [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	4,042,027	4,031,508
One- to Four-Family Segment [Member] | Correspondent Purchased [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	2,472,382	2,229,337
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	8,678	4,901
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	6,799	1,117
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	1,879	3,784
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	2,463,704	2,224,436
One- to Four-Family Segment [Member] | Bulk Purchased [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	140,065	148,477
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	1,149	2,078
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	0	921
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	1,149	1,157
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	138,916	146,399
Commercial Segment [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	1,219,685	963,156
Commercial Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	1,113,100	883,166
Commercial Segment [Member] | Commercial Real Estate [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	1,391	1,084
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	322	0
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	1,069	1,084
Commercial Segment [Member] | Commercial Real Estate [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	1,111,709	882,082
Commercial Segment [Member] | Commercial and Industrial [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	106,585	79,990
Commercial Segment [Member] | Commercial and Industrial [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	407	83
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	251	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	156	83
Commercial Segment [Member] | Commercial and Industrial [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	106,178	79,907
Consumer Segment [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	103,666	101,065
Consumer Segment [Member] | Home Equity [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	95,035	92,401
Consumer Segment [Member] | Home Equity [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	431	472
Consumer Segment [Member] | Home Equity [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	379	319
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	52	153
Consumer Segment [Member] | Home Equity [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	94,604	91,929
Consumer Segment [Member] | Other [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	8,631	8,664
Consumer Segment [Member] | Other [Member] | Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	89	27
Consumer Segment [Member] | Other [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	89	26
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	1
Consumer Segment [Member] | Other [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Amortized Cost	$ 8,542	$ 8,637