Stock-Based Compensation - Schedule of Stock-Based Compensation Expense by Type of Award (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 17.5	$ 16.1	$ 17.9
Tax benefit from stock exercised and converted during the period	7.6	2.8	9.2
Non-qualified stock options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	4.0	3.6	3.3
Restricted stock, service based (“RSUs”)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	6.4	5.8	6.4
Restricted stock, performance based (“PRSUs”)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	6.7	6.3	7.9
Employee stock purchase plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 0.4	$ 0.4	$ 0.3