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Stock-based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |
Summary of Recognized Stock-Based Compensation | The Company recognized stock-based compensation as follows:
|  | Year Ended December 31, |
|  | 2020 |  |  | 2019 |  |  | 2018 |
|  | (In thousands) |
Research and development |  | $ | 14,980 |  |  | $ | 8,031 |  |  | $ | 4,195 |
General and administrative |  |  | 15,542 |  |  |  | 8,250 |  |  |  | 2,730 |
Total stock-based compensation |  | $ | 30,522 |  |  | $ | 16,281 |  |  | $ | 6,925 |
Summary of Share-based Payment Award, Stock Options, Valuation Assumptions | The estimated grant-date fair value of all the Company’s options to purchase common stock was calculated using the Black-Scholes option pricing model, based on the following assumptions:
|  | Year Ended December 31, |
|  | 2020 |  |  | 2019 |  |  | 2018 |
Expected term (in years) |  | 5.3-6.1 |  |  | 5.3 – 6.1 |  |  | 5.1 – 6.1 |
Expected volatility |  | 74%-78% |  |  | 76% – 82% |  |  | 73% – 81% |
Risk-free interest rate |  | 0.3% - 1.8% |  |  | 1.4% – 2.6% |  |  | 2.5% – 3.1% |
Dividend yield |  | 0% |  |  | 0% |  |  | 0% |
Summary of Restricted Common Stock | Activity for the restricted common stock is shown below:
|  | Number of Shares |  |  | Weighted Average Grant Date Fair Value per Share |
Unvested restricted common stock as of December 31, 2018 |  |  | 1,917,848 |  |  | $ | 6.95 |
Vested |  |  | (866,037 | ) |  |  | 6.95 |
Forfeited |  |  | (56,973 | ) |  |  | 6.95 |
Unvested restricted common stock as of December 31, 2019 |  |  | 994,838 |  |  |  | 6.95 |
Vested |  |  | (726,659 | ) |  |  | 6.95 |
Forfeited |  |  | (81,754 | ) |  |  | 6.95 |
Unvested restricted common stock as of December 31, 2020 |  |  | 186,425 |  |  |  | 6.95 |
Summary of Options to Purchase Common Stock | Activity for the options to purchase common stock shown below:
|  | Number of Options |  |  | Weighted Average Exercise Price Per Share |  |  | Weighted Average Remaining Contractual Term |  |  | Aggregate Intrinsic Value |
|  |  |  |  |  |  |  |  |  | (In years) |  |  | (In thousands) |
Outstanding as of December 31, 2018 |  |  | 5,063,688 |  |  | $ | 8.94 |  |  |  |  |  |  |  |  |
Granted |  |  | 3,738,071 |  |  |  | 17.74 |  |  |  |  |  |  |  |  |
Exercised |  |  | (180,287 | ) |  |  | 8.43 |  |  |  |  |  |  |  |  |
Forfeited |  |  | (178,648 | ) |  |  | 11.52 |  |  |  |  |  |  |  |  |
Outstanding as of December 31, 2019 |  |  | 8,442,824 |  |  |  | 12.79 |  |  |  |  |  |  |  |  |
Granted |  |  | 5,597,148 |  |  |  | 15.35 |  |  |  |  |  |  |  |  |
Exercised |  |  | (655,772 | ) |  |  | 9.65 |  |  |  |  |  |  |  |  |
Forfeited |  |  | (729,202 | ) |  |  | 14.96 |  |  |  |  |  |  |  |  |
Outstanding as of December 31, 2020 |  |  | 12,654,998 |  |  | $ | 13.96 |  |  |  | 8.7 |  |  | $ | 39,633 |
Exercisable as of December 31, 2020 |  |  | 3,588,568 |  |  | $ | 12.74 |  |  |  | 8.1 |  |  | $ | 13,393 |
Vested and expected to vest as of December 31, 2020 |  |  | 12,654,998 |  |  | $ | 13.96 |  |  |  | 8.7 |  |  | $ | 39,633 |

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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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