Loans Receivable And Allowance For Credit Losses (Recorded Investment In Classified Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	$ 7,079,931	$ 6,966,564
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	16,540	13,956
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	46,529	45,913
One- to Four-Family Segment [Member]
Financing Receivable, Recorded Investment [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 [Line Items]
Financing receivable, total recorded investment	4,049,979	4,028,710
One- to Four-Family Segment [Member] | Originated [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	8,764	10,242
One- to Four-Family Segment [Member] | Originated [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	28,564	27,818
One- to Four-Family Segment [Member] | Correspondent Purchased [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	2,321,259	2,238,322
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	6,838	2,496
One- to Four-Family Segment [Member] | Correspondent Purchased [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	4,850	5,168
One- to Four-Family Segment [Member] | Bulk Purchased [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	402,609	418,841
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	880	1,156
One- to Four-Family Segment [Member] | Bulk Purchased [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	11,616	11,480
Commercial Real Estate Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	179,493	153,082
Commercial Real Estate Segment [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	0	0
Commercial Real Estate Segment [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	0	0
Consumer Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	126,591	127,609
Consumer Segment [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	122,378	123,345
Consumer Segment [Member] | Home Equity [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	58	54
Consumer Segment [Member] | Home Equity [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	1,469	1,431
Consumer Segment [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	4,213	4,264
Consumer Segment [Member] | Other [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	0	8
Consumer Segment [Member] | Other [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, total recorded investment	$ 30	$ 16