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Stock-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2021
Stock-Based Compensation |
Summary of stock option activity under the Equity Plans | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | Average |  | Weighted |  | Aggregate
​ | ​ | ​ |  | Exercise Price |  | Average Remaining |  | Intrinsic
​ | ​ | Options |  | Per Share | ​ | Life in Years | ​ | Value
Outstanding at December 31, 2019 | ​ | 4,024,566 | ​ | $ | 7.48 | ​ | 7.98 | ​ | $ | 2
Granted |  | 2,662,500 | ​ | $ | 2.10 |  |  |  | ​ |
Exercised |  | (32,778) | ​ | $ | 1.53 |  | ​ | ​ | ​ | ​
Forfeited | ​ | (260,435) | ​ | $ | 6.95 | ​ | ​ | ​ | ​ | ​
Outstanding at December 31, 2020 |  | 6,393,853 | ​ | $ | 5.29 |  | 7.96 | ​ | $ | 1,961
Granted |  | 2,482,650 | ​ | $ | 2.19 |  |  |  | ​ |
Exercised |  | (2,292) | ​ | $ | 1.55 |  | ​ | ​ | ​ | ​
Forfeited | ​ | (348,593) | ​ | $ | 3.17 | ​ | ​ | ​ | ​ | ​
Outstanding at December 31, 2021 | ​ | 8,525,618 | ​ | $ | 4.48 | ​ | 7.58 | ​ | $ | 7,673
Options exercisable at December 31, 2021 |  | 5,421,641 | ​ | $ | 5.83 |  | 6.89 | ​ | $ | 4,074
Options vested and expected to vest at December 31, 2021 |  | 8,525,618 | ​ | $ | 4.48 |  | 7.58 | ​ | $ | 7,673
Schedule of assumptions used to determine grant-date fair value of stock options | The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and directors during the years ended December 31, 2021 and 2020 were as follows, presented on a weighted average basis: ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31, | ​
​ |  | 2021 |  | 2020 | ​
Expected volatility |  | 67.64 | % | 66.94 | %
Weighted average risk-free interest rate |  | 0.82 | % | 0.66 | %
Expected dividend yield | ​ | 0.00 | % | 0.00 | %
Expected term (in years) | ​ | 6.82 | ​ | 6.85 | ​
Summary of RSU activity under the 2016 Plan | ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ |  | Weighted
​ |  | Number of |  | Average
​ |  | Shares |  | Fair Value
Outstanding at December 31, 2019 |  | 90,500 | ​ | $ | 1.76
Awarded | ​ | 753,106 | ​ | $ | 1.49
Settled in cash | ​ | (90,500) | ​ | $ | 1.76
Outstanding at December 31, 2020 | ​ | 753,106 | ​ | $ | 1.52
Awarded |  | 275,000 | ​ | $ | 2.57
Settled in cash |  | (92,500) | ​ | $ | 1.97
Outstanding at December 31, 2021 |  | 935,606 | ​ | $ | 1.76
Schedule of recognized stock-based compensation expense related to the issuance of stock option awards and RSUs to employees and non-employees in the condensed consolidated statements of operations | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended
​ | ​ | December 31,
​ |  | 2021 |  | 2020
Research and development |  | $ | 1,641 | ​ | $ | 1,172
General and administrative |  | ​ | 2,045 | ​ |  | 1,604
Total | ​ | $ | 3,686 | ​ | $ | 2,776

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- Definition Tabular disclosure of the number and weighted-average grant date fair value for restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock units that were granted, vested, or forfeited during the year. + 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 (c)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + 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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