Loans Receivable - Schedule of Performing or Nonperforming Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Financing Receivable, Recorded Investment [Line Items]
Total	$ 1,680,525	$ 1,435,783
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	780,831	696,896
Home Equity Loans and Lines of Credit [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	48,212	43,170
Auto Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	523	3,611
Other [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	2,002	1,716
Residential [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	713,326	623,375
Construction [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	16,768	25,024
Performing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	778,185	694,937
Performing [Member] | Home Equity Loans and Lines of Credit [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	48,165	42,832
Performing [Member] | Auto Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	523	3,590
Performing [Member] | Other [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	1,972	1,710
Performing [Member] | Residential [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	710,757	621,781
Performing [Member] | Construction [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	16,768	25,024
Nonperforming [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	2,646	1,959
Nonperforming [Member] | Home Equity Loans and Lines of Credit [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	47	338
Nonperforming [Member] | Auto Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total		21
Nonperforming [Member] | Other [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	30	6
Nonperforming [Member] | Residential [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 2,569	$ 1,594