Supporting Financial Information - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Sep. 30, 2022
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 164,542		$ 164,542		$ 65,854
Total accumulated amortization	(35,651)		(35,651)		(24,970)
Intangible assets, net	128,891		128,891		40,884
Amortization expense of intangible assets	4,100	$ 1,600	10,700	$ 4,900
Customer contracts and related customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	113,622		113,622		47,044
Total accumulated amortization	(27,087)		(27,087)		(19,731)
Covenants not to compete
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	637		637		522
Total accumulated amortization	(362)		(362)		(316)
Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	13,034		13,034		3,051
Total accumulated amortization	(1,859)		(1,859)		(1,048)
Backlog
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	37,249		37,249		15,237
Total accumulated amortization	$ (6,343)		$ (6,343)		$ (3,875)