Stock-Based Compensation (Components of Stock-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity classified awards expense	$ 1.3	$ 2.6	$ 9.0	$ 8.3
Liability classified awards expense	0.0	(0.5)	(1.1)	0.6
Total pre-tax stock-based compensation expense	1.3	2.1	7.9	8.9
Book income tax benefit	(0.5)	(0.7)	(3.0)	(3.3)
Total stock-based compensation expense, net of tax	$ 0.8	$ 1.4	$ 4.9	$ 5.6