Fair Value Measurements - Impaired Loans Remeasured and Reported at Fair Value of Underlying Collateral (Detail) - USD ($) $ in Thousands	Sep. 30, 2026	Sep. 30, 2025
Level 2 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Carrying value before allocations	$ 15,983	$ 6,719
Specific (allocations) reversals of prior allocations	(379)	(648)
Fair value	15,604	6,071
Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Carrying value before allocations	5,630	11,078
Specific (allocations) reversals of prior allocations	(474)	(706)
Fair value	$ 5,156	$ 10,372