Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Aug. 30, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 11.0	$ 2.3	$ 21.2	$ 7.7
Share price (in USD per share)	$ 35.01		$ 35.01
Stock appreciation rights
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 8.3	(0.3)	$ 10.7	1.6
Stock options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	0.3	0.3	1.0	0.6
Restricted shares, service based
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	0.9	0.9	3.3	2.5
Restricted shares, performance based
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1.3	1.3	5.7	2.7
Employee stock purchase plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 0.2	$ 0.1	$ 0.5	$ 0.3
Common Stock | Minimum
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share price (in USD per share)					$ 22
Common Stock | Maximum
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share price (in USD per share)					$ 27