Leases - Components of Total Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Finance lease expense:
Amortization of right-of-use asset	$ 0.7
Interest on lease liability	0.0
Operating lease expense:
Long-term operating lease expense	6.3
Short-term lease expense	6.9
Variable lease expense	1.6	$ 0.0
Total lease expense	$ 15.5