Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Current income tax provision (benefit)	$ (0.3)	$ (1.0)	$ 0.9	$ (0.2)
Deferred income tax provision	6.6	4.2	12.4	6.4
Total income tax provision	6.3	3.2	13.3	6.2
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected income tax provision based on federal statutory rate	7.2	3.1	11.3	3.5
State income taxes expense, net of federal tax benefit	0.8	0.3	1.3	0.3
Income tax expense (benefit) from ENLK	(2.0)	(0.3)	(1.0)	0.2
Unit-based compensation	(0.1)	0.0	1.5	2.3
Other	0.4	0.1	0.2	(0.1)
Total income tax provision	$ 6.3	$ 3.2	$ 13.3	$ 6.2