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Stock-based Compensation | 9 Months Ended
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Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |
Stock-based Compensation | 9. Stock-based Compensation During the three and nine months ended September 30, 2020 and 2019, the Company recognized the following stock-based compensation expense (in thousands):
|  | Three Months Ended September 30, |  |  | Nine Months Ended September 30, |
|  | 2020 |  |  | 2019 |  |  | 2020 |  |  | 2019 |
Research and development |  | $ | 9,109 |  |  | $ | 6,262 |  |  | $ | 24,492 |  |  | $ | 17,137 |
General and administrative |  |  | 8,131 |  |  |  | 5,081 |  |  |  | 22,596 |  |  |  | 15,063 |
Loss from equity method investment |  |  | - |  |  |  | 3,430 |  |  |  | - |  |  |  | 5,467 |
Total |  | $ | 17,240 |  |  | $ | 14,773 |  |  | $ | 47,088 |  |  | $ | 37,667 |
Stock option activity The following table summarizes stock option activity for the nine months ended September 30, 2020:
|  | Shares (in thousands) |  |  | Weighted- average exercise price per share |
Outstanding at December 31, 2019 |  |  | 7,782,437 |  |  | $ | 31.30 |
Granted |  |  | 1,468,758 |  |  | $ | 56.19 |
Exercised |  |  | (1,011,236 | ) |  | $ | 22.34 |
Cancelled or forfeited |  |  | (307,053 | ) |  | $ | 41.35 |
Outstanding at September 30, 2020 |  |  | 7,932,906 |  |  | $ | 36.66 |
Exercisable at September 30, 2020 |  |  | 3,741,338 |  |  | $ | 28.68 |
Vested and expected to vest at September 30, 2020 |  |  | 7,932,906 |  |  | $ | 36.66 |
As of September 30, 2020, total unrecognized compensation expense related to stock options was $105.5 million, which the Company expects to recognize over a remaining weighted-average period of 2.6 years. Restricted stock activity The following table summarizes restricted stock activity for the nine months ended September 30, 2020:
|  | Restricted Stock |  |  | Weighted- Average Grant Date Fair Value |
Unvested balance as of December 31, 2019 |  |  | 699,534 |  |  | $ | 56.53 |
Granted |  |  | 306,220 |  |  |  | 49.01 |
Vested |  |  | (74,583 | ) |  |  | 50.60 |
Cancelled or forfeited |  |  | (33,661 | ) |  |  | 46.23 |
Unvested balance as of September 30, 2020 |  |  | 897,510 |  |  | $ | 54.84 |
As of September 30, 2020, total unrecognized compensation expense related to unvested restricted common shares was $31.6 million, which the Company expects to recognize over a remaining weighted-average vesting period of 2.0 years.

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- Definition The entire disclosure for share-based payment arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -URI http://asc.fasb.org/topic&trid=2228938 + Details
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