Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2019

Share-based Payment Arrangement [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 nine months ended September 30, 2019 and 2018:



	Three Months Ended September 30,						Nine Months Ended September 30,
(in millions)	2019			2018			2019		2018
Stock option compensation expense	$	0.7		$	0.5		$	2.0	$	1.5
RSU compensation expense	1.2			0.8			4.1		3.7
PSU compensation expense	(1.0		)	(2.5		)	0.2		0.8
Total stock-based compensation expense	$	0.9		$	(1.2	)	$	6.3	$	6.0

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 September 30, 2019:



	September 30, 2019
	Unrecognized	Weighted Average
	Compensation	Years Expense To Be
(in millions, except weighted average years)	Expense	Recognized Over
Stock options	$4.2	2.0
RSUs	$6.8	2.0
PSUs	$5.7	2.1