Subordinated Debentures and Subordinated Notes Payable - Summary of Subordinated Debentures and Subordinated Notes Payable (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Total	$ 108,832	$ 108,636
Junior subordinated debentures payable to non-consolidated trusts
Debt Instrument [Line Items]
Amount Outstanding	75,920	75,920
Common Shares Held in Other Assets	2,520	2,520
Less: fair value adjustment	(2,088)	(2,223)
Total	73,832	73,697
Subordinated notes payable
Debt Instrument [Line Items]
Unamortized debt issuance costs	0	(61)
Total	$ 35,000	34,939
Stated interest rate (as a percent)	4.875%
GW Statutory Trust IV | Junior subordinated debentures payable to non-consolidated trusts
Debt Instrument [Line Items]
Amount Outstanding	$ 23,093	23,093
Common Shares Held in Other Assets	$ 693	$ 693
Basis spread on variable rate (as a percent)	2.85%	2.85%
GW Statutory Trust VI | Junior subordinated debentures payable to non-consolidated trusts
Debt Instrument [Line Items]
Amount Outstanding	$ 30,928	$ 30,928
Common Shares Held in Other Assets	$ 928	$ 928
Basis spread on variable rate (as a percent)	1.48%	1.48%
SSB Trust II | Junior subordinated debentures payable to non-consolidated trusts
Debt Instrument [Line Items]
Amount Outstanding	$ 2,062	$ 2,062
Common Shares Held in Other Assets	$ 62	$ 62
Basis spread on variable rate (as a percent)	1.85%	1.85%
HFB Capital Trust III | Junior subordinated debentures payable to non-consolidated trusts
Debt Instrument [Line Items]
Amount Outstanding	$ 5,155	$ 5,155
Common Shares Held in Other Assets	$ 155	$ 155
Basis spread on variable rate (as a percent)	3.35%	3.35%
HFB Capital Trust IV | Junior subordinated debentures payable to non-consolidated trusts
Debt Instrument [Line Items]
Amount Outstanding	$ 7,217	$ 7,217
Common Shares Held in Other Assets	$ 217	$ 217
Basis spread on variable rate (as a percent)	3.10%	3.10%
HFB Capital Trust V | Junior subordinated debentures payable to non-consolidated trusts
Debt Instrument [Line Items]
Amount Outstanding	$ 5,310	$ 5,310
Common Shares Held in Other Assets	$ 310	$ 310
Basis spread on variable rate (as a percent)	1.83%	1.83%
HFB Capital Trust VI | Junior subordinated debentures payable to non-consolidated trusts
Debt Instrument [Line Items]
Amount Outstanding	$ 2,155	$ 2,155
Common Shares Held in Other Assets	$ 155	$ 155
Basis spread on variable rate (as a percent)	1.65%	1.65%
Subordinated notes payable, fixed to floating rate | Subordinated notes payable
Debt Instrument [Line Items]
Amount Outstanding	$ 35,000	$ 35,000
Stated interest rate (as a percent)	3.15%	3.15%