Captive Insurance Collateral - Schedule of Captive Insurance Collateral to be Available-for-sale Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Sep. 30, 2024
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 76,088	$ 75,301
Gross Unrealized Gain	20	108
Gross Unrealized (Loss)	(424)	(558)
Fair Value	75,684	74,851
Cash and Receivables
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	454	5,741
Gross Unrealized Gain	0	0
Gross Unrealized (Loss)	0	0
Fair Value	454	5,741
U.S. Government Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	64,915	57,095
Gross Unrealized Gain	20	108
Gross Unrealized (Loss)	(59)	(104)
Fair Value	64,876	57,099
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	10,719	12,465
Gross Unrealized Gain	0	0
Gross Unrealized (Loss)	(365)	(454)
Fair Value	$ 10,354	$ 12,011