Investment Securities - Schedule of Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Sep. 30, 2022
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Due in one year or less, Amortized Cost	$ 8,255
Due after one year through five years, Amortized Cost	37,005
Due after five years through ten years, Amortized Cost	70,502
Due after ten years, Amortized Cost	102,422
Available for sale, Amortized Cost	218,184
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Due in one year or less, Fair Value	8,208
Due after one year through five years, Fair Value	35,420
Due after five years through ten years, Fair Value	63,997
Due after ten years, Fair Value	95,665
Total, Fair Value	203,290	$ 208,647
Held to maturity Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Due after five years through ten years, Amortized Cost	7,487
Due after ten years, Amortized Cost	47,417
Total, Amortized Cost	54,904
Held to maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Due after five years through ten years, Fair Value	6,553
Due after ten years, Fair Value	40,282
Total, Fair Value	$ 46,835