Stock-Based Compensation

6 Months Ended

Jun. 30, 2024

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

6. 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, 2024 and 2023:

	Three months ended June 30,				Six Months Ended June 30,
(in millions)	2024		2023		2024		2023
Stock option compensation expense	$	0.1	$	0.2	$	0.3	$	2.1
RSU compensation expense		1.4		1.3		5.0		3.6
PSU compensation expense		1.0		1.8		2.3		3.2
Total stock-based compensation expense	$	2.5	$	3.3	$	7.6	$	8.9

We generally recognize compensation expense for stock-based awards ratably over the vesting period. During the second quarter of 2024, the Company's Board of Directors approved the annual stock compensation grant to eligible non-employee directors, which consisted of 199,608 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, 2024:

	June 30, 2024
(in millions, except weighted average years)	Unrecognized Compensation Expense	Weighted Average Years Expense To Be Recognized Over
Stock options	$0.3	0.7
RSUs	$9.8	2.3
PSUs	$6.6	1.9