Supporting Financial Information - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 48,189		$ 48,189		$ 48,189
Total accumulated amortization	(10,595)		(10,595)		(6,981)
Intangible assets, net	37,594		$ 37,594		41,208
Estimated useful live of intangible assets			10 years
Amortization expense of intangible assets	1,200	$ 600	$ 3,600	$ 1,500
Customer contracts and related customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	45,600		45,600		45,600
Total accumulated amortization	(10,010)		(10,010)		(6,590)
Covenants not to compete
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	480		480		480
Total accumulated amortization	(200)		(200)		(164)
Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,109		2,109		2,109
Total accumulated amortization	$ (385)		$ (385)		$ (227)