v3.24.2
Stock-based compensation
 6 Months Ended
Jun. 30, 2024
Share-Based Payment Arrangement [Abstract]  
Stock-based compensation
11.    Stock-based compensation
The following table presents the components of stock-based compensation expense:
(in millions)
Award Classification
Three months ended June 30,
Six months ended June 30,
2024
2023
2024
2023
Stock optionsEquity$2.6 $3.6 $5.7 $7.2 
RSUsEquity8.8 5.5 17.6 14.2 
OtherBoth(0.3)0.1 0.5 0.5 
Total$11.1 $9.2 $23.8 $21.9 
Award classification:
Equity$11.6 $9.3 $24.0 $21.9 
Liability(0.5)(0.1)(0.2)— 
At June 30, 2024, unvested awards under our plans have remaining stock-based compensation expense of $103.8 million to be recognized over a weighted average period of 1.8 years.
Stock options
The following table presents information about outstanding stock options:
(options and intrinsic value in millions)
Number of optionsWeighted average exercise price per optionAggregate intrinsic valueWeighted average remaining term
Balance at December 31, 2023
16.4 $21.37 
Granted0.7 24.14 
Exercised(2.3)21.34 
Forfeited(0.7)25.94 
Balance at June 30, 2024
14.1 $21.25 $31.4 5.3 years
Expected to vest3.0 25.12 0.3 8.7 years
Vested11.1 20.24 31.1 4.4 years
During the six months ended June 30, 2024, we granted stock options that have a contractual life of ten years and will vest annually over three years, subject to the recipient continuously providing service to us through such date.
RSUs
The following table presents information about unvested RSUs:
(awards in millions)
Number of awardsWeighted average grant date fair value per award
Balance at December 31, 2023
4.0 $26.35 
Granted2.2 25.65 
Vested(0.9)25.93 
Forfeited(0.2)29.62 
Balance at June 30, 2024
5.1 $26.60 
During the six months ended June 30, 2024, we granted RSUs that will vest annually over three years, subject to the recipient continuously providing service to us throughout the vesting period. Certain of those awards contain performance and market conditions that impact the number of shares that will ultimately vest. We recorded expense on such awards of $2.7 million and $(0.5) million for the three months ended June 30, 2024 and June 30, 2023, respectively, and $4.8 million and $1.8 million for the six months ended June 30, 2024 and June 30, 2023, respectively.