Stock-Based Compensation (Components of Stock-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity classified awards expense	$ 1.5	$ 2.5	$ 7.7	$ 5.7
Liability classified awards expense	(1.3)	0.3	(1.1)	1.1
Total pre-tax stock-based compensation expense	0.2	2.8	6.6	6.8
Book income tax benefit	(0.1)	(1.1)	(2.5)	(2.6)
Total stock-based compensation expense, net of tax	$ 0.1	$ 1.7	$ 4.1	$ 4.2