Supporting Financial Information - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Sep. 30, 2021
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 65,854		$ 65,854
Total accumulated amortization	(20,031)		(18,385)
Intangible assets, net	$ 45,823		47,469
Estimated useful live of intangible assets	10 years
Amortization expense of intangible assets	$ 1,600	$ 1,600
Customer contracts and related customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	62,281		62,281
Total accumulated amortization	(18,935)		(17,378)
Covenants not to compete
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	522		522
Total accumulated amortization	(277)		(264)
Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	3,051		3,051
Total accumulated amortization	$ (819)		$ (743)