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Stock-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2023
Share-Based Payment Arrangement [Abstract] |
Summary of Stock-Based Compensation Expense | Total stock-based compensation expense recorded related to awards granted to employees and non-employees was as follows (in thousands):
|  | Year Ended December 31, |
|  | 2023 |  |  | 2022 |  |  | 2021 |
Research and development |  | $ | 10,826 |  |  | $ | 6,050 |  |  | $ | 3,492 |
General and administrative |  |  | 7,663 |  |  |  | 5,579 |  |  |  | 4,745 |
Total stock-based compensation expense |  | $ | 18,489 |  |  | $ | 11,629 |  |  | $ | 8,237 |
Summary of Activity under Plans | Activity under the Company’s 2015 and 2019 Plans and 2023 Inducement Plan is set forth below:
|  | Outstanding Options |  |  |  |  |  |  |
|  | Shares |  |  | Weighted- Average Exercise Price |  |  | Weighted- Average Remaining Contractual Term (Years) |  |  | Aggregate Intrinsic Value (in thousands) |
Balance, January 1, 2023 |  |  | 5,097,263 |  |  | $ | 12.93 |  |  |  | 7.84 |  |  | $ | 29.58 |
Options granted |  |  | 2,694,871 |  |  | $ | 18.95 |  |  |  |  |  |  |
Options exercised |  |  | (931,012 | ) |  | $ | 10.27 |  |  |  |  |  |  |
Options canceled |  |  | (591,147 | ) |  | $ | 16.93 |  |  |  |  |  |  |
Balance, December 31, 2023 |  |  | 6,269,975 |  |  | $ | 15.53 |  |  |  | 7.82 |  |  | $ | 128.49 |
Exercisable as of December 31, 2023 |  |  | 2,612,605 |  |  | $ | 12.21 |  |  |  | 6.39 |  |  | $ | 62.22 |
Vested and expected to vest as of December 31, 2023 |  |  | 6,269,975 |  |  | $ | 15.53 |  |  |  | 7.82 |  |  | $ | 128.49 |
Assumptions Used to Calculate Fair Values of Options | The fair values of options were calculated using the assumptions set forth below:
|  | Year Ended December 31,
|  | 2023 |  | 2022 |  | 2021
Expected term |  | 6.1 years |  | 6.1 years |  | 5.5 - 6.1 years
Expected volatility |  | 81.76% - 86.90% |  | 86.76% - 89.88% |  | 90.0% - 103.6%
Risk-free interest rate |  | 3.56% - 4.83% |  | 1.62% - 4.05% |  | 0.6% - 1.4%
Dividend yield |  | 0% |  | 0% |  | 0%

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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 -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 + 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 -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (d) -SubTopic 10 -Topic 718 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (e) -SubTopic 10 -Topic 718 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 + 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 -Topic 718 -SubTopic 10 -Subparagraph (f)(2) -Name Accounting Standards Codification -Paragraph 2 -Section 50 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 + Details
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