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Stock-Based Compensation (Tables) | 9 Months Ended
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Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |
Summary of Stock-Based Compensation Expense | Total stock-based compensation expense recognized was as follows (in thousands):
|  | Three Months Ended September 30, |  |  | Nine Months Ended September 30, |
|  | 2021 |  |  | 2020 |  |  | 2021 |  |  | 2020 |
Research and development |  | $ | 796 |  |  | $ | 951 |  |  | $ | 3,209 |  |  | $ | 1,125 |
General and administrative |  |  | 1,733 |  |  |  | 2,015 |  |  |  | 5,022 |  |  |  | 2,491 |
Total stock-based compensation |  | $ | 2,529 |  |  | $ | 2,966 |  |  | $ | 8,231 |  |  | $ | 3,616 |
Summary of Stock Option Activity | A summary of stock option activity for the nine months ended September 30, 2021 is set forth below:
|  | Number of Shares Available for Grant |  |  | Number of Shares Underlying Outstanding Options |  |  | Weighted- Average Exercise Price |  |  | Weighted- Average Remaining Contractual Term (in years) |  |  | Aggregate Intrinsic Value (in thousands) |
Outstanding, December 31, 2020 |  |  | 1,739,621 |  |  |  | 3,706,945 |  |  | $ | 10.90 |  |  |  | 7.98 |  |  | $ | 15,126 |
Options authorized |  |  | 2,287,089 |  |  |  | — |  |  |  |  |  |  |  |  |  |
Options granted |  |  | (2,171,632 | ) |  |  | 1,954,472 |  |  | $ | 14.89 |  |  |  |  |  |  |
Options exercised |  |  | — |  |  |  | (546,642 | ) |  | $ | 2.98 |  |  |  |  |  |  |
Options forfeited or cancelled |  |  | 838,419 |  |  |  | (838,419 | ) |  | $ | 14.15 |  |  |  |  |  |  |
Outstanding, September 30, 2021 |  |  | 2,693,497 |  |  |  | 4,276,356 |  |  | $ | 13.10 |  |  |  | 7.96 |  |  | $ | 2,101 |
Options exercisable, September 30, 2021 |  |  |  |  |  | 1,329,752 |  |  | $ | 9.77 |  |  |  | 5.33 |  |  | $ | 1,907 |
Vested and expected to vest, September 30, 2021 |  |  |  |  |  | 4,276,356 |  |  | $ | 13.10 |  |  |  | 7.96 |  |  | $ | 2,101 |
Schedule of Assumptions to Estimate Fair Value of Stock Options Using Black-Scholes Option Pricing Model | The assumptions used in the Black Scholes Model to calculate stock-based compensation are as follows:
|  | Three Months Ended September 30, |  | Nine Months Ended September 30,
|  | 2021 |  | 2020 |  | 2021 |  | 2020
Fair value of common stock |  | $7.84 - $8.35 |  | $5.96 - $10.66 |  | $7.84 - $16.82 |  | $4.85 - $10.66
Expected term (years) |  | 5.6 - 6.1 |  | 1.0 - 6.1 |  | 0.9 - 6.1 |  | 1.0 - 6.1
Volatility |  | 78.0% - 78.2% |  | 77.1% - 96.4% |  | 77.9% - 79.8% |  | 72.6% - 96.3%
Risk free rates |  | 0.9% - 1.2% |  | 0.1% - 0.4% |  | 0.1% - 1.2% |  | 0.1% - 1.7%
Dividend rate |  | 0.0% |  | 0.0% |  | 0.0% |  | 0.0%
Summary of Restricted Stock Unit Activity | The summary of RSU activity and related information follows:
|  | Number of Units Outstanding |  |  | Weighted- Average Grant Date Fair Value |
Outstanding, December 31, 2020 |  |  | — |  |  |  |
RSUs granted |  |  | 217,160 |  |  | $ | 7.37 |
RSUs Vested |  |  | — |  |  |  |
RSUs forfeited |  |  | — |  |  |  |
Outstanding, September 30, 2021 |  |  | 217,160 |  |  | $ | 7.37 |

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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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