Loans Receivable, Net and Allowance for Loan Losses - Schedule of Performing or Non-Performing Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Financing Receivable, Recorded Investment [Line Items]
Total	$ 1,386,805	$ 1,417,974
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	663,780	704,913
Home Equity Loans and Lines of Credit [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	39,094	40,800
Auto Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	24,619	39,795
Other [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	1,628	2,293
Performing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	659,994	699,837
Performing [Member] | Home Equity Loans and Lines of Credit [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	38,899	40,581
Performing [Member] | Auto Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	24,534	39,572
Performing [Member] | Other [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	1,611	2,282
Non-performing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	3,786	5,076
Non-performing [Member] | Home Equity Loans and Lines of Credit [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	195	219
Non-performing [Member] | Auto Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	85	223
Non-performing [Member] | Other [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	17	11
Residential [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	588,775	610,172
Residential [Member] | Performing [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	585,286	605,549
Residential [Member] | Non-performing [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	3,489	4,623
Construction [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	9,664	11,853
Construction [Member] | Performing [Member] | Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 9,664	$ 11,853