Loans Receivable - Classes of Loan Portfolio Summarized by Aging Categories (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current, Accruing Loans	$ 1,350,471	$ 1,423,150
31-60 Days Past Due, Accruing Loans	1,514	2,920
61-90 Days Past Due, Accruing Loans	585	941
Greater than 90 Days Due and Past Due, Accruing Loans	5,519	5,338
Total Past Due, Accruing Loans	7,618	9,199
Purchased Credit Impaired, Accruing Loans	877	1,025
Total Accruing Loans	1,358,966	1,433,374
Non-Accrual Loans	15,867	20,330
Obligations of States and Political Subdivisions [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current, Accruing Loans	56,164	79,230
Total Accruing Loans	56,164	79,230
Home Equity Loans and Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current, Accruing Loans	38,223	40,584
31-60 Days Past Due, Accruing Loans	44	48
Greater than 90 Days Due and Past Due, Accruing Loans	159	168
Total Past Due, Accruing Loans	203	216
Total Accruing Loans	38,426	40,800
Non-Accrual Loans	463	219
Auto Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current, Accruing Loans	13,576	39,056
31-60 Days Past Due, Accruing Loans	271	620
61-90 Days Past Due, Accruing Loans	5	82
Greater than 90 Days Due and Past Due, Accruing Loans		37
Total Past Due, Accruing Loans	276	739
Total Accruing Loans	13,852	39,795
Non-Accrual Loans	43	223
Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current, Accruing Loans	1,513	2,282
31-60 Days Past Due, Accruing Loans	59
Greater than 90 Days Due and Past Due, Accruing Loans	9	11
Total Past Due, Accruing Loans	68	11
Total Accruing Loans	1,581	2,293
Non-Accrual Loans	14	11
Residential [Member] | Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current, Accruing Loans	576,960	606,601
31-60 Days Past Due, Accruing Loans	1,029	979
61-90 Days Past Due, Accruing Loans	580	402
Greater than 90 Days Due and Past Due, Accruing Loans	1,744	2,190
Total Past Due, Accruing Loans	3,353	3,571
Total Accruing Loans	580,313	610,172
Non-Accrual Loans	2,865	4,623
Construction [Member] | Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current, Accruing Loans	14,013	11,853
Total Accruing Loans	14,013	11,853
Commercial [Member] | Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current, Accruing Loans	587,779	505,045
31-60 Days Past Due, Accruing Loans	111	1,218
61-90 Days Past Due, Accruing Loans		392
Greater than 90 Days Due and Past Due, Accruing Loans	2,350	1,948
Total Past Due, Accruing Loans	2,461	3,558
Purchased Credit Impaired, Accruing Loans	877	1,025
Total Accruing Loans	591,117	509,628
Non-Accrual Loans	11,124	13,426
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current, Accruing Loans	62,243	138,499
31-60 Days Past Due, Accruing Loans		55
61-90 Days Past Due, Accruing Loans		65
Greater than 90 Days Due and Past Due, Accruing Loans	1,257	984
Total Past Due, Accruing Loans	1,257	1,104
Total Accruing Loans	63,500	139,603
Non-Accrual Loans	$ 1,358	$ 1,828