Leases - Lease Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Leases [Abstract]
Operating lease costs	$ 5.1		$ 10.2
Variable lease costs	1.1		2.2
Sublease income	(0.1)		(0.2)
Total lease costs	$ 6.1	$ 5.0	12.2	$ 9.7
Operating cash flows from operating leases (fixed payments)			9.4
Operating cash flows from operating leases (liability reduction)			$ 7.6