12.   Stock-Based Compensation

Employee Equity Incentive Plan

On September 20, 2017, the Company established its 2017 Omnibus Equity Incentive Program (the “2017 Plan”) which provides for the granting of equity-based awards to certain employees, directors, independent contractors, consultants and agents. Under the 2017 Plan, the Company may grant non-qualified stock options, stock appreciation rights, restricted stock units, and other stock-based awards.

On April 19, 2021, the Company established its 2021 Omnibus Equity Incentive Plan (“2021 Equity Plan”). The 2021 Equity Plan provides for the grant of stock options (including qualified incentive stock options and nonqualified stock options), stock appreciation rights, restricted stock, restricted stock units, dividend equivalents, and other stock or cash settled incentive awards.

Stock Options

Options become exercisable subject to vesting schedules up to four years from the date of the grant and subject to certain timing restrictions upon an employee’s separation of service and no later than 10 years after the grant date.

A summary of stock option activity as of and for the six months ended June 30, 2024 is as follows:

​

​

Stock options include grants to executives that contain both market-based and performance-based vesting conditions. There were no stock options granted that contain both market-based and performance-based vesting conditions during the six months ended June 30, 2024. During the six months ended June 30, 2024, 50 stock options were exercised and 1,323 market-based and performance-based stock options remain outstanding as of June 30, 2024.

The total intrinsic value of options exercised during the six months ended June 30, 2024 and June 30, 2023 was $8.3 million and $34.1 million, respectively.

The Company’s board of directors (the “Board”) did not declare or pay dividends on any Company stock during the six months ended June 30, 2024 and June 30, 2023.

Restricted Stock Units (“RSUs”)

RSUs are subject to vesting schedules up to four years from the date of the grant and subject to certain restrictions upon employee separation.

A summary of RSUs activity as of and for the six months ended June 30, 2024 is as follows:

​

​

The total grant date fair value of RSUs that vested during the six months ended June 30, 2024 was $30.8 million.

Performance Stock Units (“PSUs”)

PSUs are subject to vesting and performance periods of up to approximately three years from the date of the grant.

A summary of PSUs activity as of and for the six months ended June 30, 2024 is as follows:

​

​

⁽¹⁾ For awards for which the performance period is complete, the number of outstanding PSUs is based on the actual shares that will vest upon completion of the service period. For awards for which the performance period is not yet complete, the number of outstanding PSUs is based on the participants earning 100% of their target PSUs.

The fair market value of PSUs with market-based and service-based vesting conditions granted for the years presented has been estimated on the grant date using the Monte Carlo Simulation model with the following assumptions:

​

​

Stock-based Compensation Expense

Total stock-based compensation expense recorded in the Condensed Consolidated Statements of Operations and Comprehensive Income was as follows:

​

​

As of June 30, 2024, unrecognized stock-based compensation expense was $203.2 million, which is expected to be recognized over a weighted-average period of 1.4 years.

Employee Stock Purchase Plan (“ESPP”)

In March 2021, the Board approved the Company’s 2021 ESPP. Purchases are accomplished through participation in discrete offering periods. The ESPP is available to U.S.-based employees and most of the Company’s non-U.S.-based employees. The current offering period began on June 1, 2024 and will end on November 30, 2024. The Company expects the program to continue consecutively for six-month offering periods for the foreseeable future.

Under the ESPP, eligible employees are able to acquire shares of the Company’s common stock by accumulating funds through payroll deductions. The purchase price for shares of common stock purchased under the ESPP is 85% of the lesser of the fair market value of the common stock on (i) the first trading day of the applicable offering period and (ii) the last trading day of the applicable offering period. Employees are required to hold shares purchased for a minimum of six months following the purchase date.

Stock-based compensation expense for the ESPP is recognized on a straight-line basis over the requisite service period of each award. Stock-based compensation expense related to the ESPP totaled $0.3 million and $0.5 million for the three and six months ended June 30, 2024, respectively. Stock-based compensation expense related to the ESPP totaled $0.2 million and $0.3 million for the three and six months ended June 30, 2023, respectively.