Captive Insurance Collateral - Schedule of Captive Insurance Collateral to be Available-for-sale Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2025	Sep. 30, 2024
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 76,775	$ 75,301
Gross Unrealized Gain	38	108
Gross Unrealized (Loss)	(317)	(558)
Fair Value	76,496	74,851
Cash and Receivables
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	120	5,741
Gross Unrealized Gain	0	0
Gross Unrealized (Loss)	0	0
Fair Value	120	5,741
U.S. Government Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	67,598	57,095
Gross Unrealized Gain	38	108
Gross Unrealized (Loss)	(19)	(104)
Fair Value	67,617	57,099
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,057	12,465
Gross Unrealized Gain	0	0
Gross Unrealized (Loss)	(298)	(454)
Fair Value	$ 8,759	$ 12,011