Allowance for Losses on Loans - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	$ 107,901	$ 108,700	$ 106,829	$ 114,591
Charge-offs	(1,938)	(2,517)	(4,059)	(5,126)
Recoveries	5,456	5,640	8,649	9,091
Provision & Transfers	(1,500)	(3,500)	(1,500)	(10,233)
Ending Allowance	109,919	108,323	109,919	108,323
Single-family residential
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	47,756	55,495	47,347	62,763
Charge-offs	(1,026)	(1,409)	(2,165)	(3,103)
Recoveries	111	4,122	2,577	6,675
Provision & Transfers	(5,013)	(3,446)	(5,931)	(11,573)
Ending Allowance	41,828	54,762	41,828	54,762
Construction
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	7,014	5,451	6,680	6,742
Charge-offs	0	0	0	(388)
Recoveries	(5)	75	150	75
Provision & Transfers	8,717	(81)	8,896	(984)
Ending Allowance	15,726	5,445	15,726	5,445
Construction - custom
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	1,062	965	990	1,695
Charge-offs	0	0	(60)	0
Recoveries	0	0	0	0
Provision & Transfers	(40)	3	92	(727)
Ending Allowance	1,022	968	1,022	968
Land - acquisition & development
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	6,778	6,671	5,781	5,592
Charge-offs	0	0	0	(38)
Recoveries	3,371	204	3,406	205
Provision & Transfers	(2,897)	530	(1,935)	1,646
Ending Allowance	7,252	7,405	7,252	7,405
Land - consumer lot loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	3,001	3,113	2,946	3,077
Charge-offs	(268)	(52)	(676)	(87)
Recoveries	0	34	0	34
Provision & Transfers	(267)	(60)	196	11
Ending Allowance	2,466	3,035	2,466	3,035
Multi-family
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	5,047	4,500	5,304	4,248
Charge-offs	0	0	0	0
Recoveries	0	0	0	220
Provision & Transfers	1,737	173	1,480	205
Ending Allowance	6,784	4,673	6,784	4,673
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	10,344	5,872	8,960	7,548
Charge-offs	(9)	0	(32)	(27)
Recoveries	992	453	1,115	481
Provision & Transfers	(3,544)	409	(2,260)	(1,268)
Ending Allowance	7,783	6,734	7,783	6,734
Commercial & industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	24,096	23,328	24,980	16,527
Charge-offs	(331)	(355)	(579)	(355)
Recoveries	590	18	591	52
Provision & Transfers	(531)	(1,845)	(1,168)	4,922
Ending Allowance	23,824	21,146	23,824	21,146
HELOC
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	820	892	902	928
Charge-offs	(26)	0	(27)	0
Recoveries	0	0	21	0
Provision & Transfers	34	(42)	(68)	(78)
Ending Allowance	828	850	828	850
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance	1,983	2,413	2,939	3,227
Charge-offs	(278)	(701)	(520)	(1,128)
Recoveries	397	734	789	1,349
Provision & Transfers	304	859	(802)	(143)
Ending Allowance	$ 2,406	3,305	$ 2,406	3,305
Covered loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Allowance				2,244
Provision & Transfers				(2,244)
Ending Allowance		$ 0		$ 0