Loans Receivable, Net and Allowance for Loan Losses - Schedule of Performing or Non-Performing Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Financing Receivable, Recorded Investment [Line Items]
Total	$ 1,291,262	$ 1,236,681
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	813,323	825,515
Purchase Credit Impaired [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	328	330
Performing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	805,505	817,506
Nonperforming [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	7,490	7,679
Residential Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	583,926	586,708
Residential Real Estate Loans [Member] | Performing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	577,491	580,116
Residential Real Estate Loans [Member] | Nonperforming [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	6,435	6,592
Commercial Real Estate Loans [Member] | Construction Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	4,072	3,097
Commercial Real Estate Loans [Member] | Performing [Member] | Construction Real Estate Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	4,072	3,097
Home Equity Loans and Lines of Credit [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	44,247	46,219
Home Equity Loans and Lines of Credit [Member] | Purchase Credit Impaired [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	328	330
Home Equity Loans and Lines of Credit [Member] | Performing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	43,615	45,576
Home Equity Loans and Lines of Credit [Member] | Nonperforming [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	304	313
Auto Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	178,420	186,646
Auto Loans [Member] | Performing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	177,698	185,910
Auto Loans [Member] | Nonperforming [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	722	736
Other [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	2,658	2,845
Other [Member] | Performing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	2,629	2,807
Other [Member] | Nonperforming [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 29	$ 38