Loans Receivable And Allowance For Credit Losses (Recorded Investment In Classified Loans) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	$ 7,234,378	$ 7,425,973
Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	63,653	69,780
Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	31,058	29,956
One- to Four-Family Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	6,294,763	6,530,681
One- to Four-Family Segment [Member] | Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	3,957,735	3,895,783
One- to Four-Family Segment [Member] | Originated [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	9,249	12,941
One- to Four-Family Segment [Member] | Originated [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	15,729	15,628
One- to Four-Family Segment [Member] | Correspondent Purchased [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	2,127,688	2,381,414
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	2,076	2,349
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	4,512	2,785
One- to Four-Family Segment [Member] | Bulk Purchased [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	209,340	253,484
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	0	102
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	5,319	5,294
Commercial Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	825,723	763,722
Commercial Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	729,437	703,139
Commercial Segment [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	50,957	52,891
Commercial Segment [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	3,541	2,472
Commercial Segment [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	96,286	60,583
Commercial Segment [Member] | Commercial and Industrial [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	1,040	1,215
Commercial Segment [Member] | Commercial and Industrial [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	1,368	3,057
Consumer Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	113,892	131,570
Consumer Segment [Member] | Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	103,829	120,436
Consumer Segment [Member] | Home Equity [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	331	280
Consumer Segment [Member] | Home Equity [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	581	696
Consumer Segment [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	10,063	11,134
Consumer Segment [Member] | Other [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	0	2
Consumer Segment [Member] | Other [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	$ 8	$ 24