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Stock-Based Compensation | 12 Months Ended
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Dec. 31, 2023
Stock-Based Compensation |
Stock-Based Compensation | Note 16. Stock-Based Compensation Stock Options We have five stock incentive plans: the 2002 Stock Incentive Plan (the “2002 Plan”), the 2009 Stock Incentive Plan (the “2009 Plan”), the 2011 Stock Incentive Plan (the “2011 Plan”), the 2015 Omnibus Equity Incentive Plan (the “2015 Plan”), and the 2018 Omnibus Equity Incentive Plan (the “2018 Plan”) (collectively, the “Plans”). The 2002 Plan, the 2009 Plan, the 2011 Plan and the 2015 Plan (the “Prior Plans”) have been superseded by the 2018 Plan. In May 2018, the stockholders approved the 2018 Plan for issuances up to an aggregate of 3,730,179 shares plus 1,269,821 shares that were authorized but unissued under the Prior Plans as of the effective date of the 2018 Plan and in April 2021, the stockholders approved an increase of 2,850,000 shares authorized under the 2018 Plan. The Prior Plans will remain in effect until all awards granted under such Prior Plans have been exercised, forfeited, cancelled, or have otherwise expired or terminated in accordance with the terms of such awards, but no awards will be made pursuant to the Prior Plans after the effectiveness of the 2018 Plan. As of December 31, 2023, the Company had 873,468 shares available for future awards under the 2018 Plan. During the years ended December 31, 2023, 2022 and 2021, we granted stock options at exercise prices equal to or greater than the quoted market price of our common stock on the grant date. The fair value of each option grant was estimated on the date of grant using Black-Scholes with the following assumptions: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, | ​
​ |  | 2023 |  | 2022 |  | 2021 | ​
Expected life (years) | ​ | 3.8 - 5.2 | ​ | 3.8 – 5.2 | ​ | 3.5 - 6.1 | ​
Risk-free interest rate |  | 3.5% - 4.4% | ​ | 2.1% - 3.7% | ​ | 0.47% - 1.18% | ​
Volatility | ​ | 69.9% - 80.0% | ​ | 67.5% – 78.6% | ​ | 64.4% – 80.8% | ​
Dividend yield |  | 0% | ​ | 0% | ​ | 0% | ​
​ The expected option life assumption is estimated based on the simplified method as the Company’s history is not indicative of future expected lives. Accordingly, the Company has utilized the average of the contractual term of the options and the weighted average vesting period for all options to calculate the expected option term. The risk-free interest rate assumption is based upon observed interest rates appropriate for the expected term of our employee stock options. The expected volatility is based on the average of the historical volatility and the implied volatility of our stock commensurate with the expected life of the stock-based award. We do not anticipate paying dividends on the common stock in the foreseeable future. We recognize stock-based compensation cost on a straight-line basis over the vesting period. Stock-based compensation expense is recognized only for those awards that ultimately vest. Forfeitures are recorded when recognized. Total stock-based compensation expense related to our share-based payment awards is comprised of the following (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | Year Ended December 31,
​ |  | 2023 |  | 2022 |  | 2021
Cost of revenues | ​ | $ | 2,216 | ​ | $ | 1,459 | ​ | $ | 1,620
Selling, general and administrative | ​ |  | 18,805 | ​ |  | 16,808 | ​ |  | 12,425
Engineering and development | ​ |  | 1,787 | ​ |  | 1,815 | ​ |  | 1,300
​ | ​ | $ | 22,808 | ​ | $ | 20,082 | ​ | $ | 15,345
​ A summary of stock option activity is as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | Weighted- | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted- | ​ | Average | ​ | ​ | ​
​ | ​ | ​ | ​ | Average | ​ | Remaining | ​ | Aggregate
​ | ​ | Number of | ​ | Exercise | ​ | Contractual | ​ | Intrinsic
​ |  | Shares |  | Price/Share |  | Term (Years) |  | Value (1)
Outstanding — December 31, 2020 |  | 7,554,305 | ​ | $ | 10.29 |  | ​ |  | ​ |
Granted (weighted-average fair value of $32.79 per share) |  | 541,353 | ​ | ​ | 56.61 |  | ​ |  | ​ |
Exercised |  | (1,037,910) |  | ​ | 8.66 |  | ​ |  | ​ |
Forfeited |  | (29,807) |  | ​ | 40.56 |  | ​ |  | ​ |
Outstanding — December 31, 2021 |  | 7,027,941 | ​ | ​ | 13.97 |  | ​ |  | ​ |
Granted (weighted-average fair value of $17.17 per share) | ​ | 589,287 | ​ | ​ | 30.12 | ​ | ​ | ​ | ​ | ​
Exercised |  | (206,898) |  | ​ | 9.90 |  | ​ |  | ​ | ​
Forfeited |  | (69,809) |  | ​ | 43.42 |  | ​ |  | ​ | ​
Outstanding — December 31, 2022 | ​ | 7,340,521 | ​ | ​ | 15.10 | ​ | ​ | ​ | ​ | ​
Granted (weighted-average fair value of $11.86 per share) | ​ | 432,990 | ​ | ​ | 20.63 | ​ | ​ | ​ | ​ | ​
Exercised |  | (407,814) |  | ​ | 3.63 |  | ​ | ​ | ​ | ​
Forfeited | ​ | (140,877) | ​ | ​ | 24.82 | ​ | ​ | ​ | ​ | ​
Outstanding — December 31, 2023 |  | 7,224,820 | ​ | $ | 15.88 |  | 4.3 | ​ | $ | 34,594
Vested (exercisable) — December 31, 2023 |  | 6,356,813 | ​ | $ | 13.88 |  | 4.1 | ​ | $ | 34,545
Expected to vest after December 31, 2023 (unexercisable) |  | 868,007 | ​ | $ | 30.55 |  | 5.7 | ​ | $ | 49
(1) | Aggregate intrinsic value represents the difference between the exercise price of the option and the closing market price of the Company’s common stock on December 29, 2023, (the last trading day of the year) which was $15.49 per share.
The following table summarizes information with respect to stock options outstanding and exercisable at December 31, 2023: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted- | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Average | ​ | Weighted- | ​ | ​ | ​ | Weighted-
​ | ​ | ​ |  | Remaining |  | Average | ​ | ​ |  | Average
​ |  | Number |  | Contractual |  | Exercise |  | Number | ​ | Exercise
Exercise Price |  | Outstanding |  | Life -Years |  | Price |  | Exercisable |  | Price
$1.87 – 3.21 |  | 729,900 |  | 2.3 | ​ | $ | 2.52 |  | 729,900 | ​ | $ | 2.52
$3.38 – 4.92 |  | 859,202 |  | 2.1 | ​ | $ | 4.35 |  | 859,202 | ​ | $ | 4.35
$5.00 – 7.89 |  | 925,116 |  | 1.6 | ​ | $ | 5.8 |  | 925,116 | ​ | $ | 5.8
$8.17 – 11.88 |  | 721,994 |  | 4.4 | ​ | $ | 9.13 |  | 721,994 | ​ | $ | 9.13
$12.53 – 15.81 |  | 910,362 |  | 5.3 | ​ | $ | 13.32 |  | 892,984 | ​ | $ | 13.33
$16.59 – 16.95 |  | 1,162,867 |  | 6.2 | ​ | $ | 16.92 |  | 1,049,018 | ​ | $ | 16.93
$17.36 – 36.68 |  | 1,319,922 |  | 5.9 | ​ | $ | 24.89 |  | 754,257 | ​ | $ | 23.75
$41.14 – 72.07 |  | 595,457 |  | 4.9 | ​ | $ | 54.70 |  | 424,342 | ​ | $ | 54.49
​ |  | 7,224,820 | ​ | ​ | ​ | ​ | ​ |  | 6,356,813 | ​ | ​ | ​
​ As of December 31, 2023, there was unrecognized compensation expense of $14.3 million related to unvested stock options, which we expect to recognize over a weighted average period of 1.9 years. The total intrinsic value of options exercised during the years ended December 31, 2023, 2022 and 2021 was $6.7 million, $5.2 million and $57.5 million, respectively. ​ Restricted stock units A summary of our restricted stock unit activity is as follows: ​
​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | Weighted Average
​ | ​ | Number of Restricted | ​ | Fair Value per
​ | ​ | Stock Units | ​ | Share
Outstanding — December 31, 2021 | ​ | 373,849 | ​ | $ | 55.53
Granted | ​ | 526,821 | ​ | ​ | 30.26
Share issuance | ​ | (101,070) | ​ | ​ | 55.43
Forfeited | ​ | (71,616) | ​ | ​ | 44.4
Outstanding – December 31, 2022 |  | 727,984 | ​ | $ | 38.32
Granted |  | 667,319 | ​ |  | 19.80
Share issuance |  | (228,932) | ​ |  | 37.63
Forfeited |  | (89,742) | ​ |  | 29.34
Outstanding – December 31, 2023 |  | 1,076,629 | ​ | $ | 27.73
​ For the years ended December 31, 2023 and 2022, we recorded stock-based compensation expense on our issued restricted stock units of $10.0 million and $7.8 million, respectively. As of December 31, 2023, there was unrecognized compensation expense of $22.2 million related to unvested restricted stock units, which we expect to recognize over a weighted average period of 2.5 years.

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