Subordinated Debentures and Subordinated Notes Payable - Summary of Subordinated Debentures and Notes Payable (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Sep. 30, 2015
Debt Instrument [Line Items]
Total	$ 108,178	$ 111,873
Junior Subordinated Debt
Debt Instrument [Line Items]
Total junior subordinated debentures payable, amount outstanding	75,920	80,920
Total junior subordinated debentures payable, common shares held in other assets	2,520	2,520
Less: fair value adjustment	(2,478)	(3,765)
Total	73,442	77,155
Junior Subordinated Debt | GW Statutory Trust IV, variable rate of 2.85%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total junior subordinated debentures payable, amount outstanding	23,093	23,093
Total junior subordinated debentures payable, common shares held in other assets	$ 693	$ 693
Basis spread on variable rate (as a percent)	2.85%	2.85%
Junior Subordinated Debt | GW Statutory Trust VI, variable rate of 1.48%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total junior subordinated debentures payable, amount outstanding	$ 30,928	$ 30,928
Total junior subordinated debentures payable, common shares held in other assets	$ 928	$ 928
Basis spread on variable rate (as a percent)	1.48%	1.48%
Junior Subordinated Debt | SSB Trust II, variable rate of 1.85%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total junior subordinated debentures payable, amount outstanding	$ 2,062	$ 2,062
Total junior subordinated debentures payable, common shares held in other assets	$ 62	$ 62
Basis spread on variable rate (as a percent)	1.85%	1.85%
Junior Subordinated Debt | HF Capital Trust III, variable rate of 3.35%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total junior subordinated debentures payable, amount outstanding	$ 5,155	$ 5,155
Total junior subordinated debentures payable, common shares held in other assets	$ 155	$ 155
Basis spread on variable rate (as a percent)	3.35%	3.35%
Junior Subordinated Debt | HF Capital Trust IV, variable rate of 3.10%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total junior subordinated debentures payable, amount outstanding	$ 7,217	$ 7,217
Total junior subordinated debentures payable, common shares held in other assets	$ 217	$ 217
Basis spread on variable rate (as a percent)	3.10%	3.10%
Junior Subordinated Debt | HF Capital Trust V, variable rate of 1.83%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total junior subordinated debentures payable, amount outstanding	$ 5,310	$ 10,310
Total junior subordinated debentures payable, common shares held in other assets	$ 310	$ 310
Basis spread on variable rate (as a percent)	1.83%	1.83%
Junior Subordinated Debt | HF Capital Trust VI, variable rate of 1.65%, plus 3 month LIBOR
Debt Instrument [Line Items]
Total junior subordinated debentures payable, amount outstanding	$ 2,155	$ 2,155
Total junior subordinated debentures payable, common shares held in other assets	$ 155	$ 155
Basis spread on variable rate (as a percent)	1.65%	1.65%
Subordinated Debt
Debt Instrument [Line Items]
Less: unamortized debt issuance costs	$ (264)	$ (282)
Total	34,736	34,718
Stated interest rate (as a percent)			4.875%
Subordinated Debt | Fixed to floating rate, 4.875% per annum
Debt Instrument [Line Items]
Total junior subordinated debentures payable, amount outstanding	$ 35,000	$ 35,000
Stated interest rate (as a percent)	4.875%	4.875%