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Stock-Based Awards (Tables) | 9 Months Ended
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Sep. 30, 2021
Share-based Payment Arrangement [Abstract] |
Summary of Stock Option Activity | The following table summarizes stock option activity for the nine months ended September 30, 2021:
| Number of Options |  | Weighted-Average Exercise Price
Balance at December 31, 2020 | 12,959,926 |  |  | $ | 16.31 |
Granted | 1,944,717 |  |  | 73.31 |
Exercised | (831,207) |  |  | 14.27 |
Forfeited | (259,060) |  |  | 34.89 |
Balance at September 30, 2021 | 13,814,376 |  |  | $ | 24.11 |
Vested and expected to vest at September 30, 2021 | 12,078,689 |  |  | $ | 27.48 |
Exercisable at September 30, 2021 | 7,856,046 |  |  | $ | 15.22 |
Summary of Assumptions Used for Estimating the Fair Value of Stock Granted | The estimated fair value of stock options granted to employees were calculated using the Black-Scholes option-pricing model using the following assumptions:
| Nine Months Ended September 30,
| 2021 |  | 2020
Expected term (in years) | 5.50 - 6.08 |  | 5.50 - 6.08
Volatility | 62.2% - 63.7% |  | 65.2% - 67.1%
Risk-free interest rate | 0.5% - 1.2% |  | 0.3% - 1.7%
Dividend yield | — |  | —
Summary of Restricted Stock Activity | The following table summarizes restricted stock unit ("RSU") activity for the nine months ended September 30, 2021:
| Number of RSU shares |  | Weighted-Average Fair Value at Date of Grant per Share
Unvested at December 31, 2020 | 2,301,679 |  |  | $ | 27.08 |
Granted | 1,046,259 |  |  | 69.50 |
Vested and released | (599,258) |  |  | 25.63 |
Forfeited | (126,827) |  |  | 60.92 |
Unvested at September 30, 2021 | 2,621,853 |  |  | $ | 43.83 |
Expected to vest at September 30, 2021 | 2,621,853 |  |  | $ | 43.83 |
Summary of Stock-Based Compensation Expense | The Company’s results of operations include expenses relating to stock-based compensation as follows (in thousands):
| Three Months Ended September 30, |  | Nine Months Ended September 30,
| 2021 |  | 2020 |  | 2021 |  | 2020
Research and development | $ | 12,174 |  |  | $ | 7,781 |  |  | $ | 36,997 |  |  | $ | 20,981 |
General and administrative | 8,824 |  |  | 5,471 |  |  | 26,165 |  |  | 15,540 |
Total | $ | 20,998 |  |  | $ | 13,252 |  |  | $ | 63,162 |  |  | $ | 36,521 |

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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=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 S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=122041274&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=120381028&loc=d3e5047-113901 + 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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- Definition Disclosure of the number and weighted-average grant date fair value for restricted stock and restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock and restricted stock units that were granted, vested, or forfeited during the year. + References No definition available. + Details
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