Loans Receivable, Net and Allowance for Credit Losses on Loans - Summary of Changes in Primary Segments of Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period			$ 18,525
Balance, End of period	$ 15,298		15,298
Allowance for credit losses	15,298		15,298		$ 18,525
Real Estate Loans [Member] | Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	4,897		4,897
Allowance for credit losses	4,897		4,897
Real Estate Loans [Member] | Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	183		183
Allowance for credit losses	183		183
Real Estate Loans [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	11,983		11,983
Allowance for credit losses	11,983		11,983
Real Estate Loans [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	941		941
Allowance for credit losses	941		941
Obligations of States and Political Subdivisions [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	110		110
Allowance for credit losses	110		110
Home Equity Loans and Lines of Credit [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	346		346
Allowance for credit losses	346		346
Auto Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	2		2
Allowance for credit losses	2		2
Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	22		22
Allowance for credit losses	22		22
Primary Segments of Allowance for Credit Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period	15,416	$ 18,315	18,525	$ 18,528
Charge-offs		(275)	(52)	(895)
Recoveries	140	30	189	137
Provision	(258)	150	(609)	450
Balance, End of period	15,298	18,220	15,298	18,220
Individually evaluated for Credit Loss	295		295		42
Collectively evaluated for Credit Loss	15,003		15,003		18,483
Allowance for credit losses	15,298	18,220	15,298	18,220	18,525	$ 18,220
Primary Segments of Allowance for Credit Losses [Member] | Impact of adopting ASC 326 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period			(2,755)
Allowance for credit losses					(2,755)
Primary Segments of Allowance for Credit Losses [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period	1,043	1,185	941	698
Charge-offs		(269)	(22)	(269)
Provision	24	53	440	540
Balance, End of period	1,067	969	1,067	969
Individually evaluated for Credit Loss	292		292
Collectively evaluated for Credit Loss	775		775		941
Allowance for credit losses	1,067	969	1,067	969	941	969
Primary Segments of Allowance for Credit Losses [Member] | Commercial Loans [Member] | Impact of adopting ASC 326 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period			(292)
Allowance for credit losses					(292)
Primary Segments of Allowance for Credit Losses [Member] | Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period		307	41	947
Provision		120		(520)
Balance, End of period	0	427	0	427
Collectively evaluated for Credit Loss					41
Allowance for credit losses	0	427	0	427	41
Primary Segments of Allowance for Credit Losses [Member] | Unallocated [Member] | Impact of adopting ASC 326 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period			(41)
Allowance for credit losses					(41)
Primary Segments of Allowance for Credit Losses [Member] | Real Estate Loans [Member] | Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period	4,953	4,870	4,897	5,122
Recoveries	3		3	2
Provision	366	(157)	(81)	(411)
Balance, End of period	5,322	4,713	5,322	4,713
Individually evaluated for Credit Loss	3		3		7
Collectively evaluated for Credit Loss	5,319		5,319		4,890
Allowance for credit losses	5,322	4,713	5,322	4,713	4,897	4,713
Primary Segments of Allowance for Credit Losses [Member] | Real Estate Loans [Member] | Residential [Member] | Impact of adopting ASC 326 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period			503
Allowance for credit losses					503
Primary Segments of Allowance for Credit Losses [Member] | Real Estate Loans [Member] | Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period	333	328	183	319
Provision	(57)	(29)	(161)	(20)
Balance, End of period	276	299	276	299
Collectively evaluated for Credit Loss	276		276		183
Allowance for credit losses	276	299	276	299	183	299
Primary Segments of Allowance for Credit Losses [Member] | Real Estate Loans [Member] | Construction [Member] | Impact of adopting ASC 326 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period			254
Allowance for credit losses					254
Primary Segments of Allowance for Credit Losses [Member] | Real Estate Loans [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period	8,031	11,016	11,983	10,754
Charge-offs		(6)	(15)	(599)
Recoveries	136		173	1
Provision	(578)	205	(823)	1,059
Balance, End of period	7,589	11,215	7,589	11,215
Individually evaluated for Credit Loss					35
Collectively evaluated for Credit Loss	7,589		7,589		11,948
Allowance for credit losses	7,589	11,215	7,589	11,215	11,983	11,215
Primary Segments of Allowance for Credit Losses [Member] | Real Estate Loans [Member] | Commercial [Member] | Impact of adopting ASC 326 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period			(3,729)
Allowance for credit losses					(3,729)
Primary Segments of Allowance for Credit Losses [Member] | Obligations of States and Political Subdivisions [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period	278	243	110	283
Provision	(9)	(1)	30	(41)
Balance, End of period	269	242	269	242
Collectively evaluated for Credit Loss	269		269		110
Allowance for credit losses	269	242	269	242	110	242
Primary Segments of Allowance for Credit Losses [Member] | Obligations of States and Political Subdivisions [Member] | Impact of adopting ASC 326 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period			129
Allowance for credit losses					129
Primary Segments of Allowance for Credit Losses [Member] | Home Equity Loans and Lines of Credit [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period	760	336	346	361
Recoveries	1	14	5	65
Provision	(6)	(18)	(19)	(94)
Balance, End of period	755	332	755	332
Collectively evaluated for Credit Loss	755		755		346
Allowance for credit losses	755	332	755	332	346	332
Primary Segments of Allowance for Credit Losses [Member] | Home Equity Loans and Lines of Credit [Member] | Impact of adopting ASC 326 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period			423
Allowance for credit losses					423
Primary Segments of Allowance for Credit Losses [Member] | Auto Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period	2	8	2	22
Charge-offs			(5)	(27)
Recoveries	0	16	8	69
Provision	0	(19)	(5)	(59)
Balance, End of period	2	5	2	5
Collectively evaluated for Credit Loss	2		2		2
Allowance for credit losses	2	5	2	5	2	5
Primary Segments of Allowance for Credit Losses [Member] | Auto Loans [Member] | Impact of adopting ASC 326 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period			2
Allowance for credit losses					2
Primary Segments of Allowance for Credit Losses [Member] | Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period	16	22	22	22
Charge-offs			(10)
Provision	2	(4)	10	(4)
Balance, End of period	18	18	18	18
Collectively evaluated for Credit Loss	18		18		22
Allowance for credit losses	$ 18	$ 18	18	$ 18	22	$ 18
Primary Segments of Allowance for Credit Losses [Member] | Other [Member] | Impact of adopting ASC 326 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period			$ (4)
Allowance for credit losses					$ (4)