Allowance for Losses on Loans - Impaired Loans Based on Loan Types (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 283,752	$ 285,243
Unpaid Principal Balance	323,299	321,743
Related Allowance	4,754	3,915
Average Recorded Investment	271,198	265,771
Amount of related allowance included in specific reserves	367	366
Amount of related allowance included in general reserves	4,387	3,549
Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	39,424	23,712
Unpaid Principal Balance	68,029	50,196
Related Allowance	0	0
Average Recorded Investment	29,752	15,479
Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	244,328	261,531
Unpaid Principal Balance	255,270	271,547
Related Allowance	4,754	3,915
Average Recorded Investment	241,446	250,292
Single-family residential
Financing Receivable, Impaired [Line Items]
Recorded Investment	227,534	237,813
Unpaid Principal Balance	233,727	243,961
Related Allowance	4,502	3,809
Average Recorded Investment	221,547	223,143
Single-family residential | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	15,488	9,627
Unpaid Principal Balance	17,258	11,366
Related Allowance	0	0
Average Recorded Investment	11,050	6,511
Single-family residential | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	212,046	228,186
Unpaid Principal Balance	216,469	232,595
Related Allowance	4,502	3,809
Average Recorded Investment	210,497	216,632
Land - acquisition & development
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,016	1,292
Unpaid Principal Balance	10,187	11,095
Related Allowance	2	1
Average Recorded Investment	1,003	2,380
Land - acquisition & development | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	165	138
Unpaid Principal Balance	8,396	9,001
Related Allowance	0	0
Average Recorded Investment	152	614
Land - acquisition & development | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	851	1,154
Unpaid Principal Balance	1,791	2,094
Related Allowance	2	1
Average Recorded Investment	851	1,766
Land - consumer lot loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	9,769	10,129
Unpaid Principal Balance	10,879	11,287
Related Allowance	41	1
Average Recorded Investment	9,527	9,865
Land - consumer lot loans | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	713	499
Unpaid Principal Balance	765	609
Related Allowance	0	0
Average Recorded Investment	525	317
Land - consumer lot loans | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	9,056	9,630
Unpaid Principal Balance	10,114	10,678
Related Allowance	41	1
Average Recorded Investment	9,002	9,548
Multi-family
Financing Receivable, Impaired [Line Items]
Recorded Investment	2,656	1,899
Unpaid Principal Balance	6,592	5,477
Related Allowance	12	13
Average Recorded Investment	2,469	2,160
Multi-family | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,160	394
Unpaid Principal Balance	5,096	3,972
Related Allowance	0	0
Average Recorded Investment	968	638
Multi-family | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,496	1,505
Unpaid Principal Balance	1,496	1,505
Related Allowance	12	13
Average Recorded Investment	1,501	1,522
Commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment	29,653	31,175
Unpaid Principal Balance	41,326	44,149
Related Allowance	197	91
Average Recorded Investment	28,931	25,571
Commercial real estate | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	11,407	11,741
Unpaid Principal Balance	19,829	21,301
Related Allowance	0	0
Average Recorded Investment	11,180	6,260
Commercial real estate | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	18,246	19,434
Unpaid Principal Balance	21,497	22,848
Related Allowance	197	91
Average Recorded Investment	17,751	19,311
Commercial & industrial
Financing Receivable, Impaired [Line Items]
Recorded Investment	11,036	1,030
Unpaid Principal Balance	17,479	3,082
Related Allowance	0	0
Average Recorded Investment	6,033	863
Commercial & industrial | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	9,680	1,030
Unpaid Principal Balance	15,065	3,082
Related Allowance	0	0
Average Recorded Investment	5,355	863
Commercial & industrial | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,356
Unpaid Principal Balance	2,414
Related Allowance	0
Average Recorded Investment	678
HELOC
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,967	1,715
Unpaid Principal Balance	2,246	1,836
Related Allowance	0	0
Average Recorded Investment	1,559	1,578
HELOC | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	767	209
Unpaid Principal Balance	1,028	315
Related Allowance	0	0
Average Recorded Investment	471	165
HELOC | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,200	1,506
Unpaid Principal Balance	1,218	1,521
Related Allowance	0	0
Average Recorded Investment	1,088	1,413
Consumer
Financing Receivable, Impaired [Line Items]
Recorded Investment	121	190
Unpaid Principal Balance	863	856
Related Allowance	0	0
Average Recorded Investment	129	211
Consumer | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	44	74
Unpaid Principal Balance	592	550
Related Allowance	0	0
Average Recorded Investment	51	111
Consumer | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	77	116
Unpaid Principal Balance	271	306
Related Allowance	0	0
Average Recorded Investment	$ 78	$ 100