Loans Receivable - Classes of Loan Portfolio Summarized by Aging Categories (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 1,409,895	$ 1,326,792
31-60 Days Past Due	2,711	3,717
61-90 Days Past Due	410	468
Non-accrual	19,541	9,007
Total Past Due	22,662	13,192
Purchased Credit Impaired, Accruing	236	243
Purchased Credit Impaired, Nonaccrual	789	1,056
Total Loans	1,433,582	1,341,283
Obligations of States and Political Subdivisions [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	79,230	71,828
Total Loans	79,230	71,828
Home Equity Loans and Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	40,533	44,319
31-60 Days Past Due	48	47
61-90 Days Past Due		168
Non-accrual	219	622
Total Past Due	267	837
Total Loans	40,800	45,156
Auto Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	38,971	80,090
31-60 Days Past Due	593	1,227
61-90 Days Past Due	8
Non-accrual	223	666
Total Past Due	824	1,893
Total Loans	39,795	81,983
Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,282	2,883
Non-accrual	11	41
Total Past Due	11	41
Total Loans	2,293	2,924
Residential [Member] | Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	604,376	590,457
31-60 Days Past Due	979	2,187
61-90 Days Past Due	402	263
Non-accrual	4,623	4,607
Total Past Due	6,004	7,057
Total Loans	610,380	597,514
Construction [Member] | Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	11,853	5,672
Total Loans	11,853	5,672
Commercial [Member] | Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	494,881	476,644
31-60 Days Past Due	1,085	236
Non-accrual	12,637	2,468
Total Past Due	13,722	2,704
Purchased Credit Impaired, Accruing	236	243
Purchased Credit Impaired, Nonaccrual	789	1,056
Total Loans	509,628	480,647
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	137,769	54,899
31-60 Days Past Due	6	20
61-90 Days Past Due		37
Non-accrual	1,828	603
Total Past Due	1,834	660
Total Loans	$ 139,603	$ 55,559