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Stock-Based Compensation

6 Months Ended

Jun. 30, 2021

Share-based Payment Arrangement [Abstract]

7. Stock-Based Compensation

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, 2021 and 2020:


	Three Months Ended June 30,				Six Months Ended June 30,
(in millions)	2021		2020		2021		2020
Stock option compensation expense	$	0.6	$	0.8	$	2.3	$	1.6

RSU compensation expense	0.9		2.0		3.4		3.0
PSU compensation expense	2.7		(0.3)		3.3		(1.2)
Total stock-based compensation expense	$	4.2	$	2.5	$	9.0	$	3.4

We generally recognize compensation expense for stock-based awards ratably over the vesting period. Stock-based compensation expense for each of the three and six months ended June 30, 2021 and 2020 includes $0.2 million and $1.0 million, of expense related to stock awards granted to eligible non-employee directors, respectively.

During the second quarter of 2021, stock compensation grants were made consisting of 19,370 stock options, 2,835 RSUs

and 11,622 PSUs and the Company's Board of Directors approved the annual stock compensation grant to eligible non-employee directors, which consisted of 83,167 RSUs.

The following table summarizes our unrecognized compensation expense and the weighted-average period over which the expense will be recognized as of June 30, 2021:


	June 30, 2021
	Unrecognized	Weighted Average
	Compensation	Years Expense To Be
(in millions, except weighted average years)	Expense	Recognized Over
Stock options	$4.6	2.2
RSUs	$5.1	1.8
PSUs	$14.0	1.9