Supporting Financial Information - Intangible Assets, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 164,542	$ 65,854
Accumulated amortization	(39,765)	(24,970)
Intangible assets, net	124,777	40,884
Customer contracts and related customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	113,622	47,044
Accumulated amortization	(29,929)	(19,731)
Backlog
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	37,249	15,237
Accumulated amortization	(7,273)	(3,875)
Trade names
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	13,034	3,051
Accumulated amortization	(2,185)	(1,048)
Covenants-not-to-compete
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	637	522
Accumulated amortization	$ (378)	$ (316)