Captive Insurance Collateral - Schedule of Captive Insurance Collateral to be Available-for-sale Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2025	Sep. 30, 2024
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 77,415	$ 75,301
Gross Unrealized Gain	203	108
Gross Unrealized (Loss)	(280)	(558)
Fair Value	77,338	74,851
Cash and Receivables
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	660	5,741
Gross Unrealized Gain	0	0
Gross Unrealized (Loss)	0	0
Fair Value	660	5,741
U.S. Government Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	67,698	57,095
Gross Unrealized Gain	203	108
Gross Unrealized (Loss)	(15)	(104)
Fair Value	67,886	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)	(265)	(454)
Fair Value	$ 8,792	$ 12,011