Loans Receivable, Net and Allowance for Loan Losses - Schedule of Performing or Non-Performing Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Sep. 30, 2021
Financing Receivable, Recorded Investment [Line Items]
Total	$ 1,339,301	$ 1,340,853
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	647,551	648,185
Home Equity Loans and Lines of Credit [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	37,384	38,426
Auto Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	10,339	13,852
Other [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	1,533	1,581
Performing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	644,786	644,800
Performing [Member] | Home Equity Loans and Lines of Credit [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	36,968	37,963
Performing [Member] | Auto Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	10,278	13,809
Performing [Member] | Other [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	1,521	1,567
Non-performing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	2,765	3,385
Non-performing [Member] | Home Equity Loans and Lines of Credit [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	416	463
Non-performing [Member] | Auto Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	61	43
Non-performing [Member] | Other [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	12	14
Residential [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	580,292	580,313
Residential [Member] | Performing [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	578,016	577,448
Residential [Member] | Non-performing [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	2,276	2,865
Construction [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	18,003	14,013
Construction [Member] | Performing [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 18,003	$ 14,013