Investment Securities - Schedule of Gross Unrealized Losses and Fair Value (Detail) $ in Thousands	Mar. 31, 2023 USD ($) Security	Sep. 30, 2022 USD ($) Security
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt \| Security	274	271
Fair Value, Less than Twelve Months, Debt	$ 80,523	$ 206,295
Gross Unrealized Losses, Less than Twelve Months, Debt	(3,202)	(20,975)
Fair Value, Twelve Months or Greater, Debt	167,303	46,874
Gross Unrealized Losses, Twelve Months or Greater, Debt	(19,788)	(6,352)
Fair Value Total, Debt	247,826	253,169
Gross Unrealized Losses Total, Debt	$ (22,990)	$ (27,327)
Fannie Mae [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt \| Security	75	74
Fair Value, Less than Twelve Months, Debt	$ 19,523	$ 67,101
Gross Unrealized Losses, Less than Twelve Months, Debt	(822)	(8,344)
Fair Value, Twelve Months or Greater, Debt	57,252	13,759
Gross Unrealized Losses, Twelve Months or Greater, Debt	(7,283)	(2,215)
Fair Value Total, Debt	76,775	80,860
Gross Unrealized Losses Total, Debt	$ (8,105)	$ (10,559)
Freddie Mac [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt \| Security	63	63
Fair Value, Less than Twelve Months, Debt	$ 26,083	$ 59,954
Gross Unrealized Losses, Less than Twelve Months, Debt	(964)	(6,868)
Fair Value, Twelve Months or Greater, Debt	41,628	9,401
Gross Unrealized Losses, Twelve Months or Greater, Debt	(5,529)	(1,806)
Fair Value Total, Debt	67,711	69,355
Gross Unrealized Losses Total, Debt	$ (6,493)	$ (8,674)
U.S. Government Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt \| Security	3	4
Fair Value, Less than Twelve Months, Debt	$ 9,373	$ 11,299
Gross Unrealized Losses, Less than Twelve Months, Debt	(135)	(670)
Fair Value, Twelve Months or Greater, Debt	2,050
Gross Unrealized Losses, Twelve Months or Greater, Debt	(392)
Fair Value Total, Debt	11,423	11,299
Gross Unrealized Losses Total, Debt	$ (527)	$ (670)
Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt \| Security	12	12
Fair Value, Less than Twelve Months, Debt	$ 1,699	$ 9,920
Gross Unrealized Losses, Less than Twelve Months, Debt	(17)	(895)
Fair Value, Twelve Months or Greater, Debt	8,469
Gross Unrealized Losses, Twelve Months or Greater, Debt	(620)
Fair Value Total, Debt	10,168	9,920
Gross Unrealized Losses Total, Debt	$ (637)	$ (895)
Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt \| Security	91	88
Fair Value, Less than Twelve Months, Debt	$ 22,920	$ 49,333
Gross Unrealized Losses, Less than Twelve Months, Debt	(1,242)	(3,394)
Fair Value, Twelve Months or Greater, Debt	47,138	19,773
Gross Unrealized Losses, Twelve Months or Greater, Debt	(5,204)	(2,193)
Fair Value Total, Debt	70,058	69,106
Gross Unrealized Losses Total, Debt	$ (6,446)	$ (5,587)
Other Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt \| Security	17	17
Fair Value, Less than Twelve Months, Debt		$ 5,764
Gross Unrealized Losses, Less than Twelve Months, Debt		(610)
Fair Value, Twelve Months or Greater, Debt	$ 6,894	1,759
Gross Unrealized Losses, Twelve Months or Greater, Debt	(567)	(84)
Fair Value Total, Debt	6,894	7,523
Gross Unrealized Losses Total, Debt	$ (567)	$ (694)
Governmental National Mortgage Association [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities, Debt \| Security	13	13
Fair Value, Less than Twelve Months, Debt	$ 925	$ 2,924
Gross Unrealized Losses, Less than Twelve Months, Debt	(22)	(194)
Fair Value, Twelve Months or Greater, Debt	3,872	2,182
Gross Unrealized Losses, Twelve Months or Greater, Debt	(193)	(54)
Fair Value Total, Debt	4,797	5,106
Gross Unrealized Losses Total, Debt	$ (215)	$ (248)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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