Investment Securities - Schedule of Gross Unrealized Losses and Fair Value (Detail) $ in Thousands	Jun. 30, 2024 USD ($) Security	Sep. 30, 2023 USD ($) Security
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt | Security	273	274
Fair Value, Less than Twelve Months, Debt	$ 28,097	$ 67,381
Gross Unrealized Losses, Less than Twelve Months, Debt	(556)	(686)
Fair Value, Twelve Months or Greater, Debt	203,146	208,884
Gross Unrealized Losses, Twelve Months or Greater, Debt	(23,299)	(31,673)
Fair Value Total, Debt	231,243	276,265
Gross Unrealized Losses Total, Debt	$ (23,855)	$ (32,359)
Fannie Mae [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt | Security	77	77
Fair Value, Less than Twelve Months, Debt	$ 4,894	$ 5,675
Gross Unrealized Losses, Less than Twelve Months, Debt	(49)	(196)
Fair Value, Twelve Months or Greater, Debt	63,247	66,220
Gross Unrealized Losses, Twelve Months or Greater, Debt	(8,451)	(11,439)
Fair Value Total, Debt	68,141	71,895
Gross Unrealized Losses Total, Debt	$ (8,500)	$ (11,635)
Freddie Mac [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt | Security	68	63
Fair Value, Less than Twelve Months, Debt	$ 10,840	$ 3,828
Gross Unrealized Losses, Less than Twelve Months, Debt	(162)	(159)
Fair Value, Twelve Months or Greater, Debt	56,068	57,168
Gross Unrealized Losses, Twelve Months or Greater, Debt	(6,946)	(9,817)
Fair Value Total, Debt	66,908	60,996
Gross Unrealized Losses Total, Debt	$ (7,108)	$ (9,976)
Governmental National Mortgage Association Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt | Security	17	14
Fair Value, Less than Twelve Months, Debt	$ 7,294	$ 2,151
Gross Unrealized Losses, Less than Twelve Months, Debt	(134)	(51)
Fair Value, Twelve Months or Greater, Debt	4,037	4,438
Gross Unrealized Losses, Twelve Months or Greater, Debt	(380)	(346)
Fair Value Total, Debt	11,331	6,589
Gross Unrealized Losses Total, Debt	$ (514)	$ (397)
U.S. Government Treasury Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt | Security		1
Fair Value, Less than Twelve Months, Debt		$ 24,705
Gross Unrealized Losses, Less than Twelve Months, Debt		(1)
Fair Value Total, Debt		24,705
Gross Unrealized Losses Total, Debt		$ (1)
U.S. Government Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt | Security	4	4
Fair Value, Less than Twelve Months, Debt	$ 1,961	$ 24,582
Gross Unrealized Losses, Less than Twelve Months, Debt	(14)	(6)
Fair Value, Twelve Months or Greater, Debt	6,486	6,304
Gross Unrealized Losses, Twelve Months or Greater, Debt	(464)	(642)
Fair Value Total, Debt	8,447	30,886
Gross Unrealized Losses Total, Debt	$ (478)	$ (648)
Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt | Security	11	11
Fair Value, Twelve Months or Greater, Debt	$ 8,535	$ 9,052
Gross Unrealized Losses, Twelve Months or Greater, Debt	(492)	(742)
Fair Value Total, Debt	8,535	9,052
Gross Unrealized Losses Total, Debt	$ (492)	$ (742)
Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt | Security	80	87
Fair Value, Less than Twelve Months, Debt	$ 3,108	$ 6,045
Gross Unrealized Losses, Less than Twelve Months, Debt	(197)	(273)
Fair Value, Twelve Months or Greater, Debt	59,556	59,677
Gross Unrealized Losses, Twelve Months or Greater, Debt	(5,977)	(7,968)
Fair Value Total, Debt	62,664	65,722
Gross Unrealized Losses Total, Debt	$ (6,174)	$ (8,241)
Other Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt | Security	16	17
Fair Value, Less than Twelve Months, Debt	$ 0	$ 395
Fair Value, Twelve Months or Greater, Debt	5,217	6,025
Gross Unrealized Losses, Twelve Months or Greater, Debt	(589)	(719)
Fair Value Total, Debt	5,217	6,420
Gross Unrealized Losses Total, Debt	$ (589)	$ (719)