Loans and Allowance for Credit Losses - Performing Loans Classified as Troubled Debt Restructuring Loans (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($) loan	Sep. 30, 2020 USD ($) loan	Jun. 30, 2021 USD ($) loan
Number of modifications | loan	1	4
Recorded Investment | $	$ 151	$ 1,974
Performing Loans
Number of modifications | loan	15		12
Recorded Investment | $	$ 3,585		$ 3,241
Residential Real Estate
Number of modifications | loan	1	1
Recorded Investment | $	$ 151	$ 98
Residential Real Estate | Performing Loans
Number of modifications | loan	3		1
Recorded Investment | $	$ 1,133		$ 895
Commercial Real Estate
Number of modifications | loan		2
Recorded Investment | $		$ 1,840
Commercial Real Estate | Performing Loans
Number of modifications | loan	5		4
Recorded Investment | $	$ 988		$ 949
Commercial loans
Number of modifications | loan		1
Recorded Investment | $		$ 36
Commercial loans | Performing Loans
Number of modifications | loan	7		7
Recorded Investment | $	$ 1,464		$ 1,397