Captive Insurance Collateral - Schedule of Captive Insurance Collateral to be Available-for-sale Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 73,921	$ 73,016
Gross Unrealized Gain	0	12
Gross Unrealized (Loss)	(1,110)	(2,311)
Fair Value	72,811	70,717
Cash and Receivables
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	26,848	4,335
Gross Unrealized Gain	0	0
Gross Unrealized (Loss)	0	0
Fair Value	26,848	4,335
U.S. Government Sponsored Agencies
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	32,377	50,471
Gross Unrealized Gain	0	0
Gross Unrealized (Loss)	(708)	(1,620)
Fair Value	31,669	48,851
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	14,696	18,210
Gross Unrealized Gain	0	12
Gross Unrealized (Loss)	(402)	(691)
Fair Value	$ 14,294	$ 17,531