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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables) | 3 Months Ended
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Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract] |
Summary of allocation of stock-based compensation expense included in operating expenses on condensed statements of operations related to share-based payment awards | The following table summarizes the stock-based compensation expense included in operating expenses on our condensed statements of operations related to stock options and employee st ock purchases for the three months ended March 31, 2021 and 2020, which was allocated as follows:
|  | Three Months Ended March 31, |
(In thousands) |  | 2021 |  |  | 2020 |
Research and development |  | $ | 825 |  |  | $ | 501 |
General and administrative |  |  | 969 |  |  |  | 1,067 |
Stock-based compensation expense included in operating expenses |  | $ | 1,794 |  |  | $ | 1,568 |
Schedule of assumptions used to estimate the fair value of service-based stock options granted | The fair value of service-based options granted during the three months ended March 31, 2021 and 2020 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions:
|  | Three Months Ended March 31, |
|  | 2021 |  | 2020 |
Dividend yield |  | 0% |  | 0% |
Expected volatility range |  | 0.779 to 0.783 |  |  | 0.781 |
Risk-free interest rate range |  | 0.51% to 0.94% |  | 1.42% to 1.62% |
Expected term |  | 5.5 yrs |  | 5.25 yrs |
Schedule of assumptions used to estimate the fair value of employee stock purchases under the purchase plan | The fair value of employees’ purchase rights during the three months ended March 31, 2021 and 2020 has been estimated using the Black Scholes option-pricing model with the following assumptions:
|  | Three Months Ended March 31,
|  | 2021 |  | 2020
Dividend yield |  | 0% |  | 0%
Expected volatility range |  | 0.507 to 0.680 |  | 0.478 to 0.564
Risk-free interest rate range |  | 0.09% to 0.16% |  | 1.56% to 1.57%
Expected term range |  | 6 mos to 12 mos |  | 6 mos to 12 mos

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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=115993241&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 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 -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 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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