Loans Receivable And Allowance For Credit Losses (Recorded Investment In Classified Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	$ 7,438,642	$ 7,425,973
Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	68,922	69,780
Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	31,263	29,956
One- to Four-Family Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	6,564,726	6,530,681
One- to Four-Family Segment [Member] | Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	3,951,004	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	12,558	12,941
One- to Four-Family Segment [Member] | Originated [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	16,901	15,628
One- to Four-Family Segment [Member] | Correspondent Purchased [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	2,374,953	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	3,102	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	3,248	2,785
One- to Four-Family Segment [Member] | Bulk Purchased [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	238,769	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	100	102
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	5,080	5,294
Commercial Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	744,674	763,722
Commercial Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	688,058	703,139
Commercial Segment [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	51,556	52,891
Commercial Segment [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	2,599	2,472
Commercial Segment [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	56,616	60,583
Commercial Segment [Member] | Commercial and Industrial [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	1,232	1,215
Commercial Segment [Member] | Commercial and Industrial [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	2,752	3,057
Consumer Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	129,242	131,570
Consumer Segment [Member] | Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	118,407	120,436
Consumer Segment [Member] | Home Equity [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	366	280
Consumer Segment [Member] | Home Equity [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	673	696
Consumer Segment [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	10,835	11,134
Consumer Segment [Member] | Other [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	8	2
Consumer Segment [Member] | Other [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, total recorded investment	$ 10	$ 24