Subordinated Debentures and Subordinated Notes Payable - Junior Subordinated Deferrable Interest Debentures (Details) $ / shares in Units, $ in Thousands	6 Months Ended
	Mar. 31, 2020 USD ($) trust $ / shares shares	Sep. 30, 2019 USD ($)
Debt Instrument [Line Items]
Total subordinated debentures and subordinated notes payable	$ 108,740	$ 108,636
Junior Subordinated Debt
Debt Instrument [Line Items]
Total subordinated debentures and subordinated notes payable	73,765	73,697
Common shares held in other assets	$ 2,520	$ 2,520
Trust Preferred Securities Subject to Mandatory Redemption
Debt Instrument [Line Items]
Number of trusts | trust	7
Number of shares caused to be issued (in shares) | shares	73,400
Par value per shares issued (in dollars per share) | $ / shares	$ 1,000
Trust Preferred Securities Subject to Mandatory Redemption | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.48%
Trust Preferred Securities Subject to Mandatory Redemption | London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	3.35%