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Stock Plans | 12 Months Ended
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Dec. 31, 2023
Stock Plans |
Stock Plans | Note 13 — Stock Plans ​ Share-based incentive awards are provided to employees under the terms of the Company’s equity incentive compensation plans (the “Plans”), which are administered by the Compensation Committee of the Board of Directors. The 2019 Plan originated as the 2010 Stock Incentive Plan and was originally approved by the Company’s shareholders in May 2010. This Plan was subsequently amended, as approved by shareholders, in 2013, 2016, 2019 (at which time the Plan was renamed the 2019 Stock Incentive Plan), and 2022 (as amended to date, the “2019 Plan”). The Company’s employees, non-employee directors, and consultants are eligible to receive awards under the 2019 Plan, which can include non-qualified stock options, incentive stock options, RSAs, RSUs, PSAs, PSUs, share appreciation rights, dividend equivalent rights, or any combination thereof. ​ The Company is authorized to issue up to 17.8 million shares under the 2019 Plan. Option awards are granted with an exercise price equal to the closing price of the Company’s common stock on the trading day prior to the date of grant; option awards generally vest over a three year period and have a seven or ten year term. RSAs and RSUs generally vest over one to five years. Certain option and share awards provide for accelerated vesting if there is a change in control, as defined in the 2019 Plan. At December 31, 2023, there is an immaterial amount of option shares and 1.7 million RSUs and PSUs outstanding under the 2019 Plan. ​ The Company is authorized to issue up to 2.25 million shares under the approved 2016 employee stock purchase plan (“ESPP”), including additional shares authorized under plan amendments approved by shareholders in 2019 and 2021. Under the ESPP, substantially all employees in the U.S. may purchase the Company’s common stock through payroll deductions at a price equal to 85 percent of the lower of the fair market value of the Company’s common stock at the beginning or end of each six-month offer period, as defined in the ESPP, and subject to certain limits. The ESPP was approved by the Company’s shareholders. ​ Shares Reserved for Future Issuance ​ At December 31, 2023, the Company has 4.5 million shares reserved to cover exercises of outstanding stock options, vesting of RSUs, and additional grants under the 2019 Plan. At December 31, 2023, the Company has 0.4 million shares reserved to cover future issuances under the ESPP Plan. ​ Share-Based Compensation ​ The Company recognized share-based compensation in the following line items in the Consolidated Statements of Operations for the periods indicated: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | For the year ended December 31,
​ |  |  | 2023 |  | 2022 |  | 2021
​ | ​ | ​ | (in thousands)
Cost of sales |  |  | $ | 4,913 |  | $ | 4,551 |  | $ | 2,373
Research and development | ​ | ​ | ​ | 8,994 | ​ | ​ | 6,682 | ​ | ​ | 3,850
Selling, general, and administrative | ​ | ​ | ​ | 14,651 | ​ | ​ | 11,761 | ​ | ​ | 9,026
Total | ​ | ​ | $ | 28,558 | ​ | $ | 22,994 | ​ | $ | 15,249
​ The Company did not realize any tax benefits associated with share-based compensation for the year ended December 31, 2021 due to the full valuation allowance on its U.S. deferred tax assets. See Note 15, “Income Taxes” for additional information. The Company recognized a tax benefit of approximately $3.9 million and $4.5 million associated with share-based compensation for the years ended December 31, 2023 and 2022, respectively. The Company capitalized an immaterial amount of share-based compensation into inventory for the years ended December 31, 2023, 2022, and 2021. ​ Unrecognized share-based compensation costs at December 31, 2023 are summarized below: ​
​ | ​ | ​ | ​ | ​ | ​
​ |  | Unrecognized |  | Weighted
​ | ​ | Share-Based | ​ | Average Period
​ | ​ | Compensation | ​ | Expected to be
​ | ​ | Costs | ​ | Recognized
​ | ​ | (in thousands) | (in years)
Restricted stock units | ​ | $ | 19,428 | ​ | 2.1
Restricted stock awards |  | ​ | 9,967 | ​ | 1.2
Performance share units |  | ​ | 7,875 | ​ | 1.8
Total unrecognized share-based compensation cost |  | $ | 37,270 | ​ | 1.8
​ Stock Option Awards ​ Stock options are awards issued to employees that entitle the holder to purchase shares of the Company’s stock at a fixed price. The following table summarizes the equity activity related to stock options: ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted
​ | ​ | Number of | ​ | Average
​ |  | Shares |  | Exercise Price
​ | ​ | (in thousands) | ​ | ​ | ​
Balance - December 31, 2020 | ​ | 730 | ​ | $ | 35.26
Exercised | ​ | (2) | ​ |  | 23.36
Expired | ​ | (285) | ​ | ​ | 40.16
Balance - December 31, 2021 | ​ | 443 | ​ | ​ | 32.15
Expired | ​ | (266) | ​ | ​ | 32.95
Balance - December 31, 2022 | ​ | 177 | ​ | ​ | 30.94
Exercised | ​ | (2) | ​ | ​ | 30.47
Expired | ​ | (165) | ​ | ​ | 30.53
Balance - December 31, 2023 | ​ | 10 | ​ | $ | 37.42
​ At December 31, 2023, stock option shares outstanding had a weighted average remaining contractual life of 0.5 years. ​ The following table summarizes information on options exercised for the periods indicated: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year ended December 31,
​ |  | 2023 |  | 2022 |  | 2021
​ | ​ | (in thousands)
Cash received from options exercised | ​ | $ | 56 | ​ | $ | — | ​ | $ | 37
Intrinsic value of options exercised | ​ | $ | 56 | ​ | $ | — | ​ | $ | 6
​ ​ RSAs, RSUs, PSAs, PSUs ​ RSAs are stock awards issued to employees and directors that are subject to specified restrictions and a risk of forfeiture. RSUs are stock awards issued to employees that entitle the holder to receive shares of common stock as the awards vest. PSAs and PSUs are awards that result in an issuance of shares of common stock to employees if certain performance or market conditions are achieved. All of these awards typically vest over one to four years and vesting is subject to the employee's continued service with the Company and, in the case of performance awards, meeting certain performance or market conditions. The fair value of the awards is determined and fixed based on the closing price of the Company’s common stock on the trading day prior to the date of grant, or, in the case of performance awards with market conditions, fair value is determined using a Monte Carlo simulation. ​ The following table summarizes the equity activity of non-vested restricted shares and performance shares: ​
​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | Weighted
​ | ​ | ​ | ​ | Average
​ | ​ | Number of | ​ | Grant Date
​ | ​ | Shares | ​ | Fair Value
​ | ​ | (in thousands) | ​ | ​ | ​
Balance - December 31, 2020 |  | 2,040 | ​ | $ | 12.73
Granted |  | 1,031 | ​ | ​ | 24.26
Performance award adjustments | ​ | 159 | ​ | ​ | 18.38
Vested |  | (1,014) | ​ | ​ | 15.50
Forfeited | ​ | (133) | ​ | ​ | 15.08
Balance - December 31, 2021 | ​ | 2,083 | ​ | ​ | 17.33
Granted | ​ | 1,253 | ​ | ​ | 29.12
Performance award adjustments | ​ | 85 | ​ | ​ | 14.03
Vested | ​ | (844) | ​ | ​ | 15.00
Forfeited | ​ | (81) | ​ | ​ | 20.18
Balance - December 31, 2022 | ​ | 2,496 | ​ | ​ | 23.83
Granted | ​ | 1,282 | ​ | ​ | 23.83
Performance award adjustments | ​ | 183 | ​ | ​ | 10.59
Vested | ​ | (1,364) | ​ | ​ | 17.47
Forfeited | ​ | (133) | ​ | ​ | 29.29
Balance - December 31, 2023 | ​ | 2,464 | ​ | $ | 26.19
​ The total fair value of shares that vested during the years ended December 31, 2023, 2022, and 2021 was $30.3 million, $22.1 million, and $22.8 million, respectively. For performance awards, the final number of shares earned will vary depending on the achievement of the actual results relative to the performance or market conditions. Each performance award is included in the table above at the grant date target share amount until the end of the performance period if not previously forfeited. ​ The fair value of performance awards with market conditions is estimated on the date of grant using a Monte Carlo simulation. Estimates of fair value are not intended to predict actual future events or the value ultimately realized by employees who receive these awards. The weighted average fair value and the assumptions used in calculating such values during fiscal years 2023, 2022, and 2021 for performance awards with market conditions were based on estimates at the date of grant as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year ended December 31, | ​
​ | ​ | 2023 |  | 2022 |  | 2021 | ​
Weighted average fair value | ​ | $ | 32.25 | ​ | $ | 45.28 | ​ | $ | 27.81 | ​
Dividend yield | ​ | ​ | 0 | % | ​ | 0 | % | ​ | 0 | %
Expected volatility factor(1) | ​ | ​ | 54 | % | ​ | 58 | % | ​ | 63 | %
Risk-free interest rate(2) | ​ | ​ | 3.84 | % | ​ | 2.13 | % | ​ | 0.34 | %
Expected life (in years)(3) | ​ | ​ | 3.0 |  | ​ | 3.0 |  | ​ | 3.0 | ​
(1) | Expected volatility is measured using historical daily price changes of the Company’s stock over the respective expected term.
(2) | The risk-free rate for periods within the contractual term is based on the U.S. Treasury yield curve in effect at the time of grant.
(3) | The expected life is the number of years the Company estimates that the awards will be outstanding prior to exercise.
​ Employee Stock Purchase Plan ​ For the years ended December 31, 2023, 2022, and 2021 the Company received cash proceeds of $4.6 million, $3.7 million, and $3.4 million, and issued shares of 258,153, 208,140, and 196,024, respectively, under the ESPP Plan. The weighted average estimated values of employee purchase rights as well as the weighted average assumptions that were used in calculating such values during fiscal years 2023, 2022, and 2021 were based on estimates at the date of grant as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year ended December 31, |
​ | ​ | 2023 |  | 2022 |  | 2021 |
Weighted average fair value | ​ | $ | 5.77 | ​ | $ | 6.00 | ​ | $ | 5.90 | ​
Dividend yield | ​ | ​ | 0 | % | ​ | 0 | % | ​ | 0 | %
Expected volatility factor(1) | ​ | ​ | 42 | % | ​ | 43 | % | ​ | 52 | %
Risk-free interest rate(2) | ​ | ​ | 5.03 | % | ​ | 1.73 | % | ​ | 0.07 | %
Expected life (in years)(3) | ​ | ​ | 0.5 |  | ​ | 0.5 |  | ​ | 0.5 | ​
(1) | Expected volatility is measured using historical daily price changes of the Company’s stock over the respective expected term.
(2) | The risk-free rate for periods within the contractual term is based on the U.S. Treasury yield curve in effect at the time of grant.
(3) | The expected life is the number of years the Company estimates that the purchase rights will be outstanding prior to exercise.
​

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