Captive Insurance Collateral - Schedule of Captive Insurance Collateral to be Available-for-sale Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 73,387	$ 73,016
Gross Unrealized Gain	14	12
Gross Unrealized (Loss)	(1,381)	(2,311)
Fair Value	72,020	70,717
Cash and Receivables
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,365	4,335
Gross Unrealized Gain	0	0
Gross Unrealized (Loss)	0	0
Fair Value	6,365	4,335
U.S. Government Sponsored Agencies
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	50,813	50,471
Gross Unrealized Gain	11	0
Gross Unrealized (Loss)	(966)	(1,620)
Fair Value	49,858	48,851
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	16,209	18,210
Gross Unrealized Gain	3	12
Gross Unrealized (Loss)	(415)	(691)
Fair Value	$ 15,797	$ 17,531