Stock-Based Compensation (Components of Stock-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Payment Arrangement [Abstract]
Equity classified awards expense	$ 1.8	$ 2.3	$ 5.9	$ 5.7
Liability classified awards expense	1.4	0.4	2.4	0.9
Total pre-tax stock-based compensation expense	3.2	2.7	8.3	6.6
Book income tax benefit	(0.9)	(0.7)	(2.2)	(1.7)
Total stock-based compensation expense, net of tax	$ 2.3	$ 2.0	$ 6.1	$ 4.9