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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables) | 9 Months Ended
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Sep. 30, 2019
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 stock purchases for the three and nine months ended September 30, 2019 and 2018, which was allocated as follows:
|  | Three Months Ended September 30, |  |  | Nine Months Ended September 30, |
(In thousands) |  | 2019 |  |  | 2018 |  |  | 2019 |  |  | 2018 |
Research and development |  | $ | 518 |  |  | $ | 269 |  |  | $ | 1,171 |  |  | $ | 690 |
General and administrative |  |  | 1,051 |  |  |  | 1,346 |  |  |  | 3,258 |  |  |  | 4,084 |
Stock-based compensation expense included in operating expenses |  | $ | 1,569 |  |  | $ | 1,615 |  |  | $ | 4,429 |  |  | $ | 4,774 |
Schedule of assumptions used to estimate the fair value of service-based and performance-based stock options granted | The fair value of service-based and performance-based options granted during the nine months ended September 30, 2019 and 2018 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions:
|  | Nine Months Ended September 30,
|  | 2019 |  | 2018
Dividend yield |  | 0% |  | 0%
Expected volatility range |  | 0.793 to 0.980 |  | 0.821 to 0.832
Risk-free interest rate range |  | 1.50% to 2.56% |  | 2.55% to 2.94%
Expected term range |  | 5.25 yrs to 6.44 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 nine months ended September 30, 2019 and 2018 has been estimated using the Black Scholes option-pricing model with the following assumptions:
|  | Nine Months Ended September 30,
|  | 2019 |  | 2018
Dividend yield |  | 0% |  | 0%
Expected volatility range |  | 0.646 to 1.653 |  | 0.437 to 0.475
Risk-free interest rate range |  | 1.94% to 2.63% |  | 1.53% to 1.76%
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=116856206&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=116856206&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=116856206&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=116856206&loc=d3e5070-113901 + Details
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