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Stock-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 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 | ​ | 1,383,410 | ​ | $ | 28.55 | ​ | ​
Exercised | ​ | (259,322) | ​ | $ | 8.72 | ​ | ​
Canceled | ​ | (88,650) | ​ | $ | 31.89 | ​ | ​
Options outstanding at December 31, 2021 | ​ | 4,077,667 | ​ | $ | 30.02 | ​ | 8.0
Options vested and expected to vest at December 31, 2021 | ​ | 3,952,611 | ​ | $ | 30.31 | ​ | 8.0
Options exercisable at December 31, 2021 | ​ | 1,483,998 | ​ | $ | 49.01 | ​ | 6.6
Shares available for grant under the 2021 Plan | ​ | 3,304,217 | ​ | ​ | ​ | ​ | ​
Schedule of stock-based compensation expense | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 2021 |  | 2020 |  | 2019
​ | ​ | (In thousands)
Research and development | ​ | $ | 4,525 | ​ | $ | 1,933 | ​ | $ | 2,053
General and administrative | ​ | ​ | 4,428 | ​ | ​ | 1,982 | ​ | ​ | 2,498
Total stock-based compensation expense | ​ | $ | 8,953 | ​ | $ | 3,915 | ​ | $ | 4,551
Schedule of assumptions used for the fair value of employee stock options granted | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 2021 |  | 2020 |  | 2019
Expected stock price volatility | ​ | 97 - 98% | ​ | 91 - 98% | ​ | 90 - 91%
Expected option term | ​ | 6.0 Years | ​ | 6.0 Years | ​ | 6.0 Years
Risk-free interest rate | ​ | 0.8 - 1.4% | ​ | 0.5 - 0.7% | ​ | 1.6 - 2.5%
Expected dividend yield | ​ | 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=122041274&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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