Loans Receivable And Allowance For Credit Losses (Recorded Investment in Loans, Past Due) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2019
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	$ 23,661	$ 21,193
Financing receivable, current loans	7,395,644	7,404,780
Financing receivable, total recorded investment	7,419,305	7,425,973
Financial Asset, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	14,573	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	9,088	6,264
One- to Four-Family Segment [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total recorded investment	6,494,393	6,530,681
One- to Four-Family Segment [Member] | Originated [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	9,070	10,448
Financing receivable, current loans	3,969,051	3,885,335
Financing receivable, total recorded investment	3,978,121	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	5,058	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	4,012	3,261
One- to Four-Family Segment [Member] | Correspondent Purchased [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	5,744	3,785
Financing receivable, current loans	2,291,891	2,377,629
Financing receivable, total recorded investment	2,297,635	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	2,963	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	2,781	1,023
One- to Four-Family Segment [Member] | Bulk Purchased [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	5,884	5,108
Financing receivable, current loans	212,753	248,376
Financing receivable, total recorded investment	218,637	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	4,579	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	1,305	1,484
Commercial Segment [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total recorded investment	807,820	763,722
Commercial Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	1,919	762
Financing receivable, current loans	707,744	702,377
Financing receivable, total recorded investment	709,663	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	1,373	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	546	0
Commercial Segment [Member] | Commercial and Industrial [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	334	243
Financing receivable, current loans	97,823	60,340
Financing receivable, total recorded investment	98,157	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	169	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	165	173
Consumer Segment [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total recorded investment	117,092	131,570
Consumer Segment [Member] | Home Equity [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	642	748
Financing receivable, current loans	106,448	119,688
Financing receivable, total recorded investment	107,090	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	393	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	249	302
Consumer Segment [Member] | Other [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, total delinquent loans	68	99
Financing receivable, current loans	9,934	11,035
Financing receivable, total recorded investment	10,002	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	38	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	$ 30	$ 21