Leases - Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Leases [Abstract]
Amortization of right of use assets - finance leases	$ 0.5	$ 1.0
Interest on lease liabilities - finance leases	0.6	1.2
Operating lease cost (cost resulting from lease payments)	3.7	6.7
Short-term lease cost	0.2	0.4
Variable lease cost (cost excluded from lease payments)	0.1	0.1
Sublease income	(0.8)	(1.6)
Total lease cost	$ 4.3	$ 7.8