Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan

The following table summarizes our stock-based compensation expense (including stock options, restricted stock units ("RSUs") and performance stock units ("PSUs")) for the three and six months ended June 30, 2019 and 2018:



	Three Months Ended June 30,				Six Months Ended June 30,
(in millions)	2019		2018		2019		2018
Stock option compensation expense	$	0.8	$	0.5	$	1.3	$	1.0
RSU compensation expense	1.9		2.0		2.9		2.9
PSU compensation expense	0.7		1.5		1.2		3.3
Total stock-based compensation expense	$	3.4	$	4.0	$	5.4	$	7.2

Schedule of Unrecognized Compensation Cost, Nonvested Awards

The following table summarizes our unrecognized compensation expense and the weighted-average period over which the expense will be recognized as of June 30, 2019:



	June 30, 2019
	Unrecognized	Weighted Average
	Compensation	Years Expense To Be
(in millions, except weighted average years)	Expense	Recognized Over
Stock options	$5.0	2.2
RSUs	$8.0	2.2
PSUs	$8.3	2.2