Credit Facilities - Summary of Loan Facilities and Subordinated Debt Financing (Details) - Secured Debt - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Loan Balance	$ 70,000,000	$ 56,000,000
Term loan
Debt Instrument [Line Items]
Loan Balance	$ 70,000,000.0
Term loan | LIBOR
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	0.035%
Debt instrument, interest rate, effective percentage	0.16%
Debt instrument, floor percentage	0.50%
Secured revolving line of credit
Debt Instrument [Line Items]
Loan Balance	$ 0
Secured revolving line of credit | LIBOR
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	0.035%
Debt instrument, interest rate, effective percentage	0.16%
Debt instrument, floor percentage	0.50%