Stock-Based Compensation (Components of Stock-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Payment Arrangement [Abstract]
Equity classified awards expense	$ 4.1	$ 4.1
Liability classified awards expense	(0.6)	1.0
Total pre-tax stock-based compensation expense	3.5	5.1
Book income tax benefit	(0.9)	(1.3)
Total stock-based compensation expense, net of tax	$ 2.6	$ 3.8