Investment Securities - Schedule of Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Sep. 30, 2021
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Due in one year or less, Amortized Cost	$ 2,758
Due after one year through five years, Amortized Cost	20,528
Due after five years through ten years, Amortized Cost	70,602
Due after ten years, Amortized Cost	73,321
Available for sale, Amortized Cost	167,209	$ 238,099
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Due in one year or less, Fair Value	2,773
Due after one year through five years, Fair Value	20,457
Due after five years through ten years, Fair Value	68,542
Due after ten years, Fair Value	71,595
Total, Fair Value	163,367	$ 240,581
Held to maturity Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Due after five years through ten years, Amortized Cost	8,513
Due after ten years, Amortized Cost	51,861
Total, Amortized Cost	60,374
Held to maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Due after five years through ten years, Fair Value	7,952
Due after ten years, Fair Value	48,180
Total, Fair Value	$ 56,132