Loans Receivable And Allowance For Credit Losses (Recorded Investment in Loans, Past Due) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	$ 40,411	$ 39,767
Financing receivable, current loans	7,039,520	6,926,797
Financing receivable, total recorded investment	7,079,931	6,966,564
Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	24,704	22,713
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	15,707	17,054
One- to Four-Family Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total recorded investment	6,773,847	6,685,873
One- to Four-Family Segment [Member] | Originated [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	17,824	21,698
Financing receivable, current loans	4,032,155	4,007,012
Financing receivable, total recorded investment	4,049,979	4,028,710
One- to Four-Family Segment [Member] | Originated [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	11,199	13,545
One- to Four-Family Segment [Member] | Originated [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	6,625	8,153
One- to Four-Family Segment [Member] | Correspondent Purchased [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	8,483	4,381
Financing receivable, current loans	2,312,776	2,233,941
Financing receivable, total recorded investment	2,321,259	2,238,322
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	7,928	3,389
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	555	992
One- to Four-Family Segment [Member] | Bulk Purchased [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	12,948	12,462
Financing receivable, current loans	389,661	406,379
Financing receivable, total recorded investment	402,609	418,841
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	4,895	5,082
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	8,053	7,380
Commercial Real Estate Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	0	0
Financing receivable, current loans	179,493	153,082
Financing receivable, total recorded investment	179,493	153,082
Commercial Real Estate Segment [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	0	0
Commercial Real Estate Segment [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	0	0
Consumer Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total recorded investment	126,591	127,609
Consumer Segment [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	1,121	1,155
Financing receivable, current loans	121,257	122,190
Financing receivable, total recorded investment	122,378	123,345
Consumer Segment [Member] | Home Equity [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	665	635
Consumer Segment [Member] | Home Equity [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	456	520
Consumer Segment [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	35	71
Financing receivable, current loans	4,178	4,193
Financing receivable, total recorded investment	4,213	4,264
Consumer Segment [Member] | Other [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	17	62
Consumer Segment [Member] | Other [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, total delinquent loans	$ 18	$ 9