Loans Receivable And Allowance For Credit Losses (Recorded Investment in Loans, Past Due) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	$ 20,557	$ 21,193
Financing receivable, current loans	7,213,821	7,404,780
Financing receivable, total recorded investment	7,234,378	7,425,973
Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	9,172	14,929
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	11,385	6,264
One- to Four-Family Segment [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total recorded investment	6,294,763	6,530,681
One- to Four-Family Segment [Member] | Originated [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	7,348	10,448
Financing receivable, current loans	3,950,387	3,885,335
Financing receivable, total recorded investment	3,957,735	3,895,783
One- to Four-Family Segment [Member] | Originated [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	3,001	7,187
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]
Financing receivable, total delinquent loans	4,347	3,261
One- to Four-Family Segment [Member] | Correspondent Purchased [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	5,603	3,785
Financing receivable, current loans	2,122,085	2,377,629
Financing receivable, total recorded investment	2,127,688	2,381,414
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	3,170	2,762
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]
Financing receivable, total delinquent loans	2,433	1,023
One- to Four-Family Segment [Member] | Bulk Purchased [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	5,496	5,108
Financing receivable, current loans	203,844	248,376
Financing receivable, total recorded investment	209,340	253,484
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	2,558	3,624
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]
Financing receivable, total delinquent loans	2,938	1,484
Commercial Segment [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total recorded investment	825,723	763,722
Commercial Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	1,246	762
Financing receivable, current loans	728,191	702,377
Financing receivable, total recorded investment	729,437	703,139
Commercial Segment [Member] | Commercial Real Estate [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	40	762
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]
Financing receivable, total delinquent loans	1,206	0
Commercial Segment [Member] | Commercial and Industrial [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	162	243
Financing receivable, current loans	96,124	60,340
Financing receivable, total recorded investment	96,286	60,583
Commercial Segment [Member] | Commercial and Industrial [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	5	70
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]
Financing receivable, total delinquent loans	157	173
Consumer Segment [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total recorded investment	113,892	131,570
Consumer Segment [Member] | Home Equity [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	619	748
Financing receivable, current loans	103,210	119,688
Financing receivable, total recorded investment	103,829	120,436
Consumer Segment [Member] | Home Equity [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	323	446
Consumer Segment [Member] | Home Equity [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	296	302
Consumer Segment [Member] | Other [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	83	99
Financing receivable, current loans	9,980	11,035
Financing receivable, total recorded investment	10,063	11,134
Consumer Segment [Member] | Other [Member] | Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	75	78
Consumer Segment [Member] | Other [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	$ 8	$ 21