Stock-Based Compensation

3 Months Ended

Mar. 31, 2022

Share-based Payment Arrangement [Abstract]

Stock-Based Compensation

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 months ended March 31, 2022 and 2021:

		Three Months Ended March 31,
(in millions)		2022			2021
Stock option compensation expense	$		2.1	$		1.7
RSU compensation expense			2.1			2.5
PSU compensation expense			0.7			0.6
Total stock-based compensation expense	$		4.9	$		4.8

We generally recognize compensation expense for stock-based awards ratably over the vesting period. During the first quarter of 2022, the Compensation and Human Committee of the Company's Board of Directors approved stock compensation grants which consisted of 1,652,413 stock options, 498,659 RSUs and 458,957 PSUs.

The following table summarizes our unrecognized compensation expense and the weighted-average period over which the expense will be recognized as of March 31, 2022:

	March 31, 2022
(in millions, except weighted average years)	Unrecognized Compensation Expense	Weighted Average Years Expense To Be Recognized Over
Stock options	$5.3	2.6
RSUs	$5.4	2.5
PSUs	$9.1	2.1