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Stock-Based Compensation (Tables) | 6 Months Ended
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Jun. 30, 2021
Stock-Based Compensation |
Schedule of fair value assumptions of stock options | ​
​ | ​ | ​ | ​
Expected life (years) | ​ | 3.5 – 6.1 |
Risk-free interest rate | ​ | 0.5% - 0.9 | %
Volatility | ​ | 64.4% - 80.8 | %
Dividend yield | ​ | 0 | %
Schedule of share-based payment awards | 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. Total stock-based compensation expense related to all of our share-based payment awards is comprised of the following: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended June 30, | ​ | Six Months Ended June 30, | ​
​ |  | 2021 |  | 2020 |  | 2021 |  | 2020 |
Cost of revenues | ​ | $ | 452 | ​ | $ | 83 | ​ | $ | 691 | ​ | $ | 151 | ​
Selling, general and administrative | ​ |  | 3,222 | ​ | ​ | 2,043 | ​ |  | 5,727 | ​ |  | 3,488 | ​
Engineering and development | ​ |  | 350 | ​ | ​ | 175 | ​ |  | 597 | ​ |  | 283 | ​
​ | ​ | $ | 4,024 | ​ | $ | 2,301 | ​ | $ | 7,015 | ​ | $ | 3,922 | ​
Schedule of stock option activity | 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 $32.61 per share) |  | 504,671 | ​ | ​ | 56.18 |  |  |  | ​ |
Exercised |  | (386,242) |  | ​ | 9.02 |  |  |  | ​ |
Forfeited |  | (16.224) |  | ​ | 23.97 |  |  |  | ​ |
Outstanding — June 30, 2021 |  | 7,656,510 | ​ | $ | 13.35 |  | 6.2 | ​ | $ | 381,115
Vested (exercisable) — June 30, 2021 |  | 5,890,689 | ​ | $ | 8.26 |  | 5.6 | ​ | $ | 323,018
Expected to vest after June 30, 2021 (unexercisable) |  | 1,765,821 | ​ | $ | 30.30 |  | 8.3 | ​ | $ | 57,914
(1) | Aggregate intrinsic value represents the difference between the exercise price of the option and the closing market price of our common stock on June 30, 2021, which was $63.10 per share.
Schedule of restricted stock unit activity | 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, 2020 |  | — |  | $ | —
Granted |  | 345,571 | ​ |  | 54.61
Forfeited | ​ | (6,359) | ​ | ​ | 53.58
Share issuance |  | — | ​ |  | —
Outstanding June 30, 2021 |  | 339,212 | ​ | $ | 54.63

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- Definition Tabular disclosure of activity for award under share-based payment arrangement. Includes, but is not limited to, outstanding award at beginning and end of year, granted, exercised, forfeited, and weighted-average grant date fair value. + 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) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + 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 (d) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=120381028&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=120381028&loc=d3e5070-113901 + Details
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