Loan Servicing Rights - Summary of Fair Values (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Freddie Mac
Servicing Assets at Fair Value [Line Items]
Mortgage servicing rights (MSR), fair value	$ 3,656,000	$ 3,120,000	$ 3,694,000
Mortgage servicing rights (MSR), average discount rates for estimating fair value	9.00%	9.00%	9.00%
Mortgage servicing rights (MSR), average conditional prepayment rates for estimating fair value	0.1271	0.1442	0.1131
MSRs valuation allowances	$ 119,000	$ 211,000	$ 0
SBA
Servicing Assets at Fair Value [Line Items]
Mortgage servicing rights (MSR), fair value	$ 99,000	$ 115,000	$ 202,000
Mortgage servicing rights (MSR), average discount rates for estimating fair value	15.00%
Mortgage servicing rights (MSR), average conditional prepayment rates for estimating fair value	0.1785	0.1629	0.1613
MSRs valuation allowances	$ 0	$ 18,000	$ 8,000