Stock-Based Compensation

6 Months Ended

Jun. 30, 2022

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, 2022 and 2021:


		Three months ended June 30,						Six Months Ended June 30,
(in millions)		2022			2021			2022			2021
Stock option compensation expense	$		0.6	$		0.6	$		2.7	$		2.3
RSU compensation expense			0.9			0.9			3.0			3.4
PSU compensation expense			0.8			2.7			1.5			3.3
Total stock-based compensation expense	$		2.3	$		4.2	$		7.2	$		9.0

We generally recognize compensation expense for stock-based awards ratably over the vesting period.

During the second quarter of 2022, stock compensation grants were made consisting of 127,174 stock options, 38,153 RSUs and 703,379 PSUs. Also the Company's Board of Directors approved the annual stock compensation grant to eligible non-employee directors, which consisted of 132,632 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, 2022:


	June 30, 2022
(in millions, except weighted average years)	Unrecognized Compensation Expense	Weighted Average Years Expense To Be Recognized Over
Stock options	$4.9	2.3
RSUs	$5.7	2.2
PSUs	$11.0	2.1