Loans Receivable - Summary of Changes in Primary Segments of Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period	$ 18,525
Balance, End of period	15,306	$ 18,525
Allowance for credit losses	15,306	18,525
Real Estate Loans [Member] | Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	4,897
Allowance for credit losses	4,897
Real Estate Loans [Member] | Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	183
Allowance for credit losses	183
Real Estate Loans [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	11,983
Allowance for credit losses	11,983
Real Estate Loans [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	941
Allowance for credit losses	941
Obligations of States and Political Subdivisions [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	110
Allowance for credit losses	110
Home Equity Loans and Lines of Credit [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	346
Allowance for credit losses	346
Auto Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	2
Allowance for credit losses	2
Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, End of period	22
Allowance for credit losses	22
Primary Segments of Allowance for Credit Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, Beginning of period	18,525	18,528
Charge-offs	(84)	(912)
Recoveries	220	209
Provision	(600)	700
Balance, End of period	15,306	18,525
Individually evaluated for Credit Loss	2	42
Collectively evaluated for Credit Loss	15,304	18,483
Allowance for credit losses	15,306	18,525
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)
Balance, End 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	941	698
Charge-offs	(22)	(269)
Provision	133	512
Balance, End of period	760	941
Collectively evaluated for Credit Loss	760	941
Allowance for credit losses	760	941
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)
Balance, End 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	41	947
Provision		(906)
Balance, End of period		41
Collectively evaluated for Credit Loss		41
Allowance for credit losses		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)
Balance, End 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	4,897	5,122
Recoveries	14	45
Provision	(35)	(270)
Balance, End of period	5,379	4,897
Individually evaluated for Credit Loss	2	7
Collectively evaluated for Credit Loss	5,377	4,890
Allowance for credit losses	5,379	4,897
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
Balance, End 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	183	319
Provision	(169)	(136)
Balance, End of period	268	183
Collectively evaluated for Credit Loss	268	183
Allowance for credit losses	268	183
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
Balance, End 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	11,983	10,754
Charge-offs	(15)	(615)
Recoveries	188	20
Provision	(612)	1,824
Balance, End of period	7,815	11,983
Individually evaluated for Credit Loss		35
Collectively evaluated for Credit Loss	7,815	11,948
Allowance for credit losses	7,815	11,983
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)
Balance, End 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	110	283
Provision	42	(173)
Balance, End of period	281	110
Collectively evaluated for Credit Loss	281	110
Allowance for credit losses	281	110
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
Balance, End 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	346	361
Charge-offs	(32)
Recoveries	6	66
Provision	30	(81)
Balance, End of period	773	346
Collectively evaluated for Credit Loss	773	346
Allowance for credit losses	773	346
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
Balance, End 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	22
Charge-offs	(5)	(28)
Recoveries	12	78
Provision	(9)	(70)
Balance, End of period	2	2
Collectively evaluated for Credit Loss	2	2
Allowance for credit losses	2	2
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
Balance, End 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	22	22
Charge-offs	(10)
Provision	20
Balance, End of period	28	22
Collectively evaluated for Credit Loss	28	22
Allowance for credit losses	28	22
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)
Balance, End of period		(4)
Allowance for credit losses		$ (4)