Supporting Financial Information - Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Sep. 30, 2024
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	$ 164,542	$ 164,542
Total accumulated amortization	(60,335)	(56,221)
Intangible assets, net	104,207	108,321
Customer contracts and related customer relationships
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	113,622	113,622
Total accumulated amortization	(44,139)	(41,297)
Covenants-not-to-compete
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	637	637
Total accumulated amortization	(458)	(442)
Trade name
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	13,034	13,034
Total accumulated amortization	(3,814)	(3,488)
Backlog
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	37,249	37,249
Total accumulated amortization	$ (11,924)	$ (10,994)