Income Taxes - Components of Income Tax Benefit (Provision) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Current income tax expense	$ (0.4)	$ (0.3)	$ (0.7)	$ (1.3)
Deferred income tax benefit (expense)	(11.3)	5.7	22.7	4.9
Income tax benefit (expense)	(11.7)	5.4	22.0	3.6
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected income tax benefit (expense) based on federal statutory rate	(3.7)	4.5	63.6	41.2
State income tax benefit (expense), net of federal benefit	(1.0)	0.4	7.0	4.3
Unit-based compensation	(6.8)	(0.1)	(4.4)	0.0
Non-deductible expense related to goodwill impairment	0.0	0.0	(43.4)	(43.8)
Other	(0.2)	0.6	(0.8)	1.9
Income tax benefit (expense)	$ (11.7)	$ 5.4	$ 22.0	$ 3.6