Loans Receivable, Net and Allowance for Loan Losses - Classes of Loan Portfolio, Internal Risk Rating System (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Sep. 30, 2022
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	$ 1,569,338	$ 1,435,783
Commercial And Municipal Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	841,246	757,415
Commercial And Municipal Portfolio Segment | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	748,379	678,841
Commercial And Municipal Portfolio Segment | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	44,823	38,158
Commercial And Municipal Portfolio Segment | Obligations of States and Political Subdivisions [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	48,044	40,416
Commercial And Municipal Portfolio Segment | Pass [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	824,483	734,842
Commercial And Municipal Portfolio Segment | Pass [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	734,312	659,104
Commercial And Municipal Portfolio Segment | Pass [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	42,127	35,322
Commercial And Municipal Portfolio Segment | Pass [Member] | Obligations of States and Political Subdivisions [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	48,044	40,416
Commercial And Municipal Portfolio Segment | Special Mention [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	4,809	7,750
Commercial And Municipal Portfolio Segment | Special Mention [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	3,270	6,060
Commercial And Municipal Portfolio Segment | Special Mention [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	1,539	1,690
Commercial And Municipal Portfolio Segment | Substandard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	11,954	14,823
Commercial And Municipal Portfolio Segment | Substandard [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	10,797	13,677
Commercial And Municipal Portfolio Segment | Substandard [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loan, total	$ 1,157	$ 1,146