Stock-Based Compensation (Components of Stock-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation, equity classified awards	$ 3.2	$ 2.4
Stock-based compensation, liability classified awards	0.8	0.3
Total pre-tax stock-based compensation expense	4.0	2.7
Book income tax benefit	(1.5)	(1.0)
Total stock-based compensation expense, net of tax	$ 2.5	$ 1.7