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Stock-Based Compensation (Tables) | 3 Months Ended
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Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Schedule of performance-based awards |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Period Granted | ​ | Options Granted | ​ | RSUs Granted | ​ | Options Vested | ​ | RSUs Vested | ​ | Milestone | ​ | Valuation Method
(in thousands)
Q1 2019 | ​ | 200 | ​ | 300 | ​ | 169 | ​ | 260 | ​ | (1) | ​ | Monte-Carlo Simulation
Q2 2019 | ​ | — | ​ | 188 | ​ | — | ​ | 81 | ​ | (2) | ​ | Fair Market Value
Q3 2019 | ​ | — | ​ | 50 | ​ | — | ​ | 38 | ​ | (1) | ​ | Monte-Carlo Simulation
Q1 2020 | ​ | 150 | ​ | 300 | ​ | 75 | ​ | 150 | ​ | (1) | ​ | Monte-Carlo Simulation
Q1 2020 | ​ | — | ​ | 436 | ​ | — | ​ | 9 | ​ | (3) | ​ | Fair Market Value
Q1 2020 | ​ | 129 | ​ | — | ​ | — | ​ | — | ​ | (3) | ​ | Black-Scholes-Merton
Q2 2020 | ​ | — | ​ | 21 | ​ | — | ​ | — | ​ | (3) | ​ | Fair Market Value
Q3 2020 | ​ | 10 | ​ | — | ​ | 10 | ​ | — | ​ | (4) | ​ | Black-Scholes-Merton
Q3 2020 | ​ | — | ​ | 27 | ​ | — | ​ | 5 | ​ | (3) | ​ | Fair Market Value
Q4 2020 | ​ | — | ​ | 32 | ​ | — | ​ | 6 | ​ | (1) | ​ | Monte-Carlo Simulation
Q4 2020 | ​ | — | ​ | 22 | ​ | — | ​ | 2 | ​ | (5) | ​ | Fair Market Value
Q1 2021 | ​ | 150 | ​ | 125 | ​ | — | ​ | — | ​ | (1) | ​ | Monte-Carlo Simulation
Q1 2021 | ​ | — | ​ | 279 | ​ | — | ​ | 10 | ​ | (3) | ​ | Fair Market Value
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
________________________________ (1) The awards will vest based on the achievement of certain values of the Company’s common stock at multiple thresholds within certain periods and are contingent upon the completion of requisite service through the date of such vesting. ​ (2) The vesting of the awards will be triggered after the end of the achievement milestone, as measured by the Company. ​ (3) The awards will vest based on achievement of a revenue target and are contingent upon the completion of requisite service through the date of such vesting. ​ (4) The awards vest based on achievement of a reimbursement target.
​ (5) The awards will vest based on achievement of certain revenue and recruiting targets.
Summary of stock option activity | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Outstanding Options
​ |  | ​ |  | ​ |  | ​ |  | Weighted- |  | ​
​ | ​ | ​ | ​ | ​ | ​ | Weighted- | ​ | Average | ​ | ​
​ | ​ | Shares | ​ | ​ | ​ | Average | ​ | Remaining | ​ | Aggregate
​ | ​ | Available for | ​ | Number of | ​ | Exercise | ​ | Contractual | ​ | Intrinsic
(in thousands, except for contractual life and exercise price) | ​ | Grant | ​ | Shares | ​ | Price | ​ | Life | ​ | Value
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | (in years) | ​ | ​
Balance at December 31, 2020 |  | 3,197 |  | 6,707 | ​ | $ | 11.19 | ​ | 6.04 | ​ | $ | 592,468
Additional shares authorized |  | 3,446 | ​ | — | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Options granted |  | (150) |  | 150 | ​ | $ | 119.73 | ​ | ​ | ​ | ​ | ​
Options exercised |  | — |  | (575) | ​ | $ | 7.95 | ​ | ​ | ​ | ​ | ​
Options forfeited/cancelled |  | 17 |  | (17) | ​ | $ | 12.64 | ​ | ​ | ​ | ​ | ​
RSUs granted | ​ | (1,180) | ​ | — | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
RSUs forfeited/cancelled | ​ | 78 | ​ | — | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Balance at March 31, 2021 |  | 5,408 |  | 6,265 | ​ | $ | 14.09 | ​ | 5.98 | ​ | $ | 550,649
Exercisable at March 31, 2021 | ​ | ​ |  | 4,796 | ​ | $ | 9.51 | ​ | 5.34 | ​ | $ | 441,349
Vested and expected to vest at March 31, 2021 | ​ | ​ |  | 6,176 | ​ | $ | 13.87 | ​ | 5.95 | ​ | $ | 544,020
Restricted stock units | ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted-
​ | ​ | ​ | ​ | Average
​ | ​ | ​ | ​ | Grant Date
(in thousands, except for grant date fair value) | ​ | Shares | ​ | Fair Value
​ | ​ | ​ | ​ | ​ | ​
Balance at December 31, 2020 | ​ | 4,188 | ​ | $ | 34.02
Granted | ​ | 1,180 | ​ | $ | 103.94
Vested | ​ | (632) | ​ | $ | 26.17
Cancelled/forfeited | ​ | (78) | ​ | $ | 35.35
Balance at March 31, 2021 | ​ | 4,658 | ​ | $ | 52.38
Performance-based awards |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Schedule of assumptions used in valuation of fair value | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | March 31,
​ | 2021
Risk-free interest rate | ​ | 0.80 | ​ | — | 0.95 | %
Expected dividend yield | ​ | ​ | ​ | ​ | 0.00 | %
Expected volatility | ​ | ​ | ​ | ​ | 60 | %
Expected term (years) | ​ | 7.25 | ​ | — | 10.00 | ​
Employee and non-employee stock options |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Summary of stock-based compensation expenses | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three months ended March 31,
​ | ​ | 2021 | ​ | 2020
​ |  | Employee |  | Non-Employee |  | Total |  | Employee |  | Non-Employee |  | Total
​ | ​ | (in thousands)
Cost of revenues | ​ | $ | 708 | ​ | $ | — | ​ | $ | 708 | ​ | $ | 314 | ​ | $ | — | ​ | $ | 314
Research and development | ​ |  | 3,650 | ​ |  | 224 | ​ |  | 3,874 | ​ |  | 1,682 | ​ |  | 160 | ​ |  | 1,842
Selling, general and administrative | ​ |  | 18,604 | ​ |  | 46 | ​ |  | 18,650 | ​ |  | 5,252 | ​ |  | 9 | ​ |  | 5,261
Total | ​ | $ | 22,962 | ​ | $ | 270 | ​ | $ | 23,232 | ​ | $ | 7,248 | ​ | $ | 169 | ​ | $ | 7,417
Employee stock options |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Schedule of assumptions used in valuation of fair value | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three months ended March 31, | ​
​ |  | 2021 |  |  | 2020 |  | ​
Expected term (years) |  | ​ | ​ | ​ | 10.00 | ​ |  | 5.27 | ​ | — | 10.00 | ​ | ​
Expected volatility |  | ​ | ​ | ​ | 55.33 | % |  | 49.94 | % | — | 58.53 | % | ​
Expected dividend rate |  | ​ | ​ | ​ | 0 | % |  | ​ | ​ | ​ | 0 | % | ​
Risk-free interest rate |  | ​ | ​ | ​ | 1.13 | % |  | 0.44 | % | — | 1.70 | % | ​

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- Definition Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901 + Details
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- Definition Tabular disclosure of number, weighted-average exercise price or conversion ratio, aggregate intrinsic value, and weighted-average remaining contractual term for outstanding restricted stock units that are fully vested and expected to vest. Includes, but is not limited to, unvested restricted stock units for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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