Supporting Financial Information - Intangible Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Sep. 30, 2025
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	$ 164,542	$ 164,542
Total accumulated amortization	(80,904)	(72,677)
Intangible assets, net	$ 83,638	91,865
Intangible assets, remaining amortization period	6 years 1 month 6 days
Customer contracts and related customer relationships
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	$ 113,622	113,622
Total accumulated amortization	$ (58,349)	(52,665)
Intangible assets, remaining amortization period	6 years 1 month 6 days
Backlog
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	$ 37,249	37,249
Total accumulated amortization	$ (16,575)	(14,714)
Intangible assets, remaining amortization period	5 years 10 months 24 days
Trade name
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	$ 13,034	13,034
Total accumulated amortization	$ (5,443)	(4,792)
Intangible assets, remaining amortization period	6 years 3 months 18 days
Covenants-not-to-compete
Finite-Lived Intangible Assets [Line Items]
Total intangible assets	$ 637	637
Total accumulated amortization	$ (537)	$ (506)
Intangible assets, remaining amortization period	6 years