Allowance for Losses on Loans - Impaired Loans Based on Loan Types (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Mar. 31, 2016	Sep. 30, 2015
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 291,139	$ 341,579
Unpaid Principal Balance	322,378	381,223
Related Allowance	4,459	6,678
Average Recorded Investment	290,774	333,815
Amount of related allowance included in specific reserves	1,036	275
Amount of related allowance included in general reserves	3,423	6,403
Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	20,831	38,866
Unpaid Principal Balance	43,054	70,564
Related Allowance	0	0
Average Recorded Investment	18,258	29,474
Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	270,308	302,713
Unpaid Principal Balance	279,324	310,659
Related Allowance	4,459	6,678
Average Recorded Investment	272,516	304,341
Single-family residential
Financing Receivable, Impaired [Line Items]
Recorded Investment	245,362	276,711
Unpaid Principal Balance	251,075	282,912
Related Allowance	4,277	6,678
Average Recorded Investment	244,605	274,097
Single-family residential | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	11,818	17,250
Unpaid Principal Balance	13,412	19,644
Related Allowance	0	0
Average Recorded Investment	10,345	14,069
Single-family residential | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	233,544	259,461
Unpaid Principal Balance	237,663	263,268
Related Allowance	4,277	6,678
Average Recorded Investment	234,260	260,028
Construction
Financing Receivable, Impaired [Line Items]
Recorded Investment		5,441
Unpaid Principal Balance		7,929
Related Allowance		0
Average Recorded Investment		5,903
Construction | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment		453
Unpaid Principal Balance		2,151
Related Allowance		0
Average Recorded Investment		471
Construction | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment		4,988
Unpaid Principal Balance		5,778
Related Allowance		0
Average Recorded Investment		5,432
Construction - custom
Financing Receivable, Impaired [Line Items]
Recorded Investment	699	554
Unpaid Principal Balance	759	554
Related Allowance	0	0
Average Recorded Investment	449	182
Construction - custom | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	699	554
Unpaid Principal Balance	759	554
Related Allowance	0	0
Average Recorded Investment	449	182
Land - acquisition & development
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,820	5,056
Unpaid Principal Balance	11,920	12,852
Related Allowance	24	0
Average Recorded Investment	2,232	4,404
Land - acquisition & development | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	188	2,570
Unpaid Principal Balance	9,086	9,426
Related Allowance	0	0
Average Recorded Investment	365	926
Land - acquisition & development | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,632	2,486
Unpaid Principal Balance	2,834	3,426
Related Allowance	24	0
Average Recorded Investment	1,867	3,478
Land - consumer lot loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	10,529	12,016
Unpaid Principal Balance	11,671	12,368
Related Allowance	7	0
Average Recorded Investment	10,914	11,868
Land - consumer lot loans | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	548	727
Unpaid Principal Balance	634	814
Related Allowance	0	0
Average Recorded Investment	418	544
Land - consumer lot loans | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	9,981	11,289
Unpaid Principal Balance	11,037	11,554
Related Allowance	7	0
Average Recorded Investment	10,496	11,324
Multi-family
Financing Receivable, Impaired [Line Items]
Recorded Investment	2,566	7,593
Unpaid Principal Balance	6,315	10,877
Related Allowance	11	0
Average Recorded Investment	2,202	5,277
Multi-family | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,044	3,770
Unpaid Principal Balance	4,793	7,054
Related Allowance	0	0
Average Recorded Investment	675	1,545
Multi-family | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,522	3,823
Unpaid Principal Balance	1,522	3,823
Related Allowance	11	0
Average Recorded Investment	1,527	3,732
Commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment	27,936	28,551
Unpaid Principal Balance	31,014	36,698
Related Allowance	140	0
Average Recorded Investment	27,767	27,016
Commercial real estate | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	5,797	9,427
Unpaid Principal Balance	6,428	15,620
Related Allowance	0	0
Average Recorded Investment	4,891	8,130
Commercial real estate | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	22,139	19,124
Unpaid Principal Balance	24,586	21,078
Related Allowance	140	0
Average Recorded Investment	22,876	18,886
Commercial & industrial
Financing Receivable, Impaired [Line Items]
Recorded Investment	182	2,955
Unpaid Principal Balance	6,611	13,066
Related Allowance	0	0
Average Recorded Investment	567	2,681
Commercial & industrial | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	182	2,955
Unpaid Principal Balance	6,611	13,066
Related Allowance	0	0
Average Recorded Investment	567	2,681
HELOC
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,835	2,126
Unpaid Principal Balance	2,228	2,975
Related Allowance	0	0
Average Recorded Investment	1,724	1,895
HELOC | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	439	683
Unpaid Principal Balance	830	1,532
Related Allowance	0	0
Average Recorded Investment	330	536
HELOC | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,396	1,443
Unpaid Principal Balance	1,398	1,443
Related Allowance	0	0
Average Recorded Investment	1,394	1,359
Consumer
Financing Receivable, Impaired [Line Items]
Recorded Investment	210	576
Unpaid Principal Balance	785	992
Related Allowance	0	0
Average Recorded Investment	314	492
Consumer | Financing Receivable, Impairment, No Related Allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	116	477
Unpaid Principal Balance	501	703
Related Allowance	0	0
Average Recorded Investment	218	390
Consumer | Financing Receivable, Impairment, Allowance Recorded
Financing Receivable, Impaired [Line Items]
Recorded Investment	94	99
Unpaid Principal Balance	284	289
Related Allowance	0	0
Average Recorded Investment	$ 96	$ 102