Leases - Lease Obligations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other non-current assets:
Finance leases - ROU assets	$ 44.5		$ 44.5
Finance leases - Accumulated depreciation	(11.5)		(11.5)
Operating leases - ROU assets	90.8		90.8
Operating leases - Accumulated depreciation	(13.9)		(13.9)
Total lease assets	109.9		109.9
Current portion of long-term debt:
Finance leases	(7.9)		(7.9)
Operating leases	(23.7)		(23.7)
Long-term debt, less current portion:
Finance leases	(27.3)		(27.3)
Operating leases	(55.4)		(55.4)
Unrealized gain on derivative instruments, net of taxes	(4.5)	$ 23.6	1.0	$ 13.7
Total lease liabilities	$ (114.3)		$ (114.3)