Supporting Financial Information - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Sep. 30, 2021
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 65,854		$ 65,854	$ 65,854
Total accumulated amortization	(21,677)		(21,677)	(18,385)
Intangible assets, net	44,177		$ 44,177	47,469
Estimated useful live of intangible assets			10 years
Amortization expense of intangible assets	1,600	$ 1,600	$ 3,300
Customer contracts and related customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	62,281		62,281	62,281
Total accumulated amortization	(20,492)		(20,492)	(17,378)
Covenants not to compete
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	522		522	522
Total accumulated amortization	(290)		(290)	(264)
Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	3,051		3,051	3,051
Total accumulated amortization	$ (895)		$ (895)	$ (743)