Income Taxes - Schedule of Income Tax Expense (Benefit) Differs from Amount Computed at Federal Statutory Corporate Tax Rate (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2017	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Federal tax at statutory rate		$ (8.1)	$ 12.0	$ (20.0)
State tax, net of federal tax expense (benefit)		(0.4)	1.5	(5.2)
Tax effect of:
Equity-based compensation		1.1	1.0	2.4
Provision to return and deferred tax adjustments			(0.9)	(0.6)
Non-deductible promotional and entertainment expense		0.5	0.8	1.0
Fuel tax credit and other credits		(0.6)	(0.8)	(0.7)
Change in uncertain tax positions		(1.3)	(0.8)	0.6
Non-deductible IPO costs				1.6
Domestic production activities deduction	[1]			(1.7)
Rate change	[2]		0.1	(43.4)
Other, net		(0.4)	(0.1)	(0.2)
Total income tax expense (benefit)		$ (9.2)	$ 12.8	$ (66.2)

[1] In 2018, the Company calculated refund claims related to the domestic production activities deduction. The refund claims reduced the tax provision by $1.7. The domestic production activities deduction was eliminated by the 2017 Tax Act.

[2] In 2018, the inclusion of the revaluation of the net deferred tax liability attributable to the 2017 Tax Act reduced the tax provision by $43.4.