Stock-Based Compensation (Components of Stock-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Payment Arrangement [Abstract]
Equity classified awards expense	$ 2.4	$ 2.4	$ 8.3	$ 8.1
Liability classified awards expense	0.2	1.4	2.6	2.3
Total pre-tax stock-based compensation expense	2.6	3.8	10.9	10.4
Book income tax benefit	(0.6)	(1.0)	(2.8)	(2.7)
Total stock-based compensation expense, net of tax	$ 2.0	$ 2.8	$ 8.1	$ 7.7