Supporting Financial Information - Intangible Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Sep. 30, 2024
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	$ 164,542	$ 164,542
Total accumulated amortization	(68,563)	(56,221)
Intangible assets, net	95,979	108,321
Customer contracts and related customer relationships
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	113,622	113,622
Total accumulated amortization	(49,823)	(41,297)
Backlog
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	37,249	37,249
Total accumulated amortization	(13,784)	(10,994)
Trade name
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	13,034	13,034
Total accumulated amortization	(4,466)	(3,488)
Covenants-not-to-compete
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	637	637
Total accumulated amortization	$ (490)	$ (442)