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Stock-Based Compensation (Tables) | 9 Months Ended
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Sep. 30, 2021
Stock-Based Compensation |
Schedule of stock option activity | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted | ​ | Weighted
​ | ​ | ​ | ​ | Average | ​ | Average
​ | ​ | ​ | ​ | Exercise | ​ | Remaining
​ | ​ | ​ | ​ | Price | ​ | Contractual
​ |  | Shares |  | Per Share |  | Term (In Years)
Options outstanding at December 31, 2020 |  | 3,042,229 | ​ | $ | 28.93 | ​ | 8.2
Granted |  | 1,350,210 | ​ | $ | 28.16 | ​ | ​
Exercised |  | (192,464) | ​ | $ | 9.53 | ​ | ​
Canceled |  | (70,349) | ​ | $ | 35.62 | ​ | ​
Options outstanding at September 30, 2021 |  | 4,129,626 | ​ | $ | 29.46 | ​ | 8.2
Options vested and expected to vest at September 30, 2021 |  | 3,982,965 | ​ | $ | 29.81 | ​ | 8.2
Options exercisable at September 30, 2021 |  | 1,387,147 | ​ | $ | 51.75 | ​ | 6.7
Shares available for grant under the 2021 Plan |  | 3,319,116 | ​ | ​ | ​ | ​ | ​
​
Schedule of stock-based compensation expense | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three months ended September 30, | ​ | Nine months ended September 30,
​ |  | 2021 |  | 2020 |  | 2021 |  | 2020
​ | ​ | (In thousands) | ​ | (In thousands)
Research and development | ​ | $ | 1,504 | ​ | $ | 642 | ​ | $ | 2,927 | ​ | $ | 1,294
General and administrative | ​ |  | 1,525 | ​ |  | 608 | ​ |  | 2,886 | ​ |  | 1,364
Total stock-based compensation expense | ​ | $ | 3,029 | ​ | $ | 1,250 | ​ | $ | 5,813 | ​ | $ | 2,658
​
Schedule of assumptions used for the fair value of employee stock options granted | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three months ended September 30, | ​ | Nine months ended September 30,
|  | 2021 | ​ | 2020 |  | 2021 |  | 2020
Expected stock price volatility |  | 98% | ​ | 98% | ​ | 97 – 98% | ​ | 91 – 98%
Expected option term |  | 6.0 Years | ​ | 6.0 Years | ​ | 6.0 Years | ​ | 6.0 Years
Risk-free interest rate |  | 1.1 – 1.2% | ​ | 0.5% | ​ | 0.8 – 1.3% | ​ | 0.5 – 0.6%
Expected dividend yield |  | None | ​ | None | ​ | None | ​ | None

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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 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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