Stock-Based Compensation (Components of Stock-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Payment Arrangement [Abstract]
Equity classified awards expense	$ 2.5	$ 2.4	$ 9.2	$ 8.3
Liability classified awards expense	1.1	0.2	0.6	2.6
Total pre-tax stock-based compensation expense	3.6	2.6	9.8	10.9
Book income tax benefit	(0.9)	(0.6)	(2.4)	(2.8)
Total stock-based compensation expense, net of tax	$ 2.7	$ 2.0	$ 7.4	$ 8.1