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STOCK-BASED COMPENSATION (Tables) | 12 Months Ended
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Dec. 31, 2023
Share-Based Payment Arrangement [Abstract] |
Schedule of Stock-Based Compensation Expense | The following table shows total stock-based compensation expense recognized in the accompanying Consolidated Statements of Operations (in thousands):
| Year Ended December 31,
| 2023 |  | 2022 |  | 2021
Research and development | $ | 15,215 |  |  | $ | 18,404 |  |  | $ | 19,534 |
General and administrative | 12,148 |  |  | 13,246 |  |  | 13,422 |
Total stock-based compensation expense | $ | 27,363 |  |  | $ | 31,650 |  |  | $ | 32,956 |
Schedule of Assumptions used for Estimating Fair Value of Employee Stock Options | The assumptions used for estimating the fair value of the employee stock options were as follows:
| Year Ended December 31,
| 2023 |  | 2022 |  | 2021
Risk-free interest rate | 3.44-4.00% |  | 2.15-3.69% |  | 0.95-1.22%
Expected term (in years) | 5.47-5.56 |  | 5.46-5.49 |  | 5.46-5.52
Expected dividend yield of stock | — |  |  | — |  |  | — |
Expected volatility | 72.18-76.05% |  | 72.38-76.01% |  | 77.30-79.77%
Schedule of Assumptions used for Estimating the Fair Value of the ESPP Purchase Rights | The assumptions used for estimating the fair value of the ESPP purchase rights are as follows:
| Year Ended December 31,
| 2023 |  | 2022 |  | 2021
Risk-free interest rate | 4.28-5.37% |  | 1.62-4.61% |  | 0.01-2.80%
Expected term (in years) | 0.5-2.0 |  | 0.5-2.0 |  | 0.0-2.0
Expected dividend yield of stock | — |  |  | — |  |  | — |
Expected volatility | 65.71-100.60% |  | 57.97-72.14% |  | 32.54-97.88%

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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of employee stock purchase plans, including, but not limited to: (a) expected term, (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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- 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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