Supporting Financial Information - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 48,189		$ 48,189		$ 48,189
Total accumulated amortization	(9,390)		(9,390)		(6,981)
Intangible assets, net	38,799		$ 38,799		41,208
Estimated useful live of intangible assets			10 years
Amortization expense of intangible assets	1,200	$ 400	$ 2,400	$ 900
Customer contracts and related customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	45,600		45,600		45,600
Total accumulated amortization	(8,870)		(8,870)		(6,590)
Covenants not to compete
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	480		480		480
Total accumulated amortization	(188)		(188)		(164)
Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,109		2,109		2,109
Total accumulated amortization	$ (332)		$ (332)		$ (227)