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Stockholders' Equity (Tables) | 9 Months Ended
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Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Schedule of Summarizes Stock Option Activities | The following table summarizes stock option activities for the nine months ended September 30, 2021: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ | ​ |  | Weighted Average
​ | ​ | ​ | ​ | ​ | ​ | ​ | Remaining
​ | ​ | ​ | ​ | Weighted Average | ​ | Contractual Life (in
​ | ​ | Stock Options | ​ | Exercise Price | ​ | years)
Outstanding at December 31, 2020 |  | 1,141,675 | ​ | $ | 5.73 |  | 6.31
Outstanding at September 30, 2021 |  | 1,141,675 | ​ |  | 5.73 |  | 5.56
Options vested and exercisable at September 30, 2021 |  | 713,547 | ​ | $ | 5.73 |  | 5.56
Schedule of Stock-Based Compensation Expense | The following table summarizes stock-based compensation expense for the three and nine months ended September 30, 2021 and 2020 (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | For the three months ended September 30, | ​ | For the nine months ended September 30, | ​
​ |  | 2021 |  | 2020 |  | 2021 |  | 2020 |
General and administrative | ​ | $ | 229 | ​ | $ | 348 | ​ | $ | 793 | ​ | $ | 1,213 | ​
Research and development | ​ |  | 655 | ​ |  | 258 | ​ |  | 1,634 | ​ |  | 1,155 | ​
Total stock-based compensation expense | ​ | $ | 884 | ​ | $ | 606 | ​ | $ | 2,427 | ​ | $ | 2,368 | ​
Summary of Warrant Activities | A summary of warrant activities for the nine months ended September 30, 2021, is presented below: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ | ​ |  | Weighted Average
​ | ​ | ​ | ​ | ​ | ​ | ​ | Remaining
​ | ​ | ​ | ​ | Weighted Average | ​ | Contractual Life (in
​ | ​ | Warrants | ​ | Exercise Price | ​ | years)
Outstanding as of December 31, 2020 |  | 5,402,670 | ​ | $ | 8.21 |  | 1.39
Expired |  | (666,366) | ​ |  | 8.50 |  | —
Cashless exercised |  | (138) | ​ |  | — |  | —
Outstanding as of September 30, 2021 |  | 4,736,166 | ​ | $ | 8.16 |  | 0.73
Restricted Stock Awards [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Schedules of Restricted Stock and Restricted Stock Unit Activity | The following table summarizes restricted stock award activities for the nine months ended September 30, 2021: ​
​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | Weighted Average
​ | ​ | ​ | ​ | Grant Date Fair
​ | ​ | Number of Shares | ​ | Value
Nonvested at December 31, 2020 |  | 302,114 | ​ | $ | 4.93
Granted |  | 68,870 | ​ |  | 3.63
Vested | ​ | (90,001) | ​ | ​ | 6.69
Nonvested at September 30, 2021 |  | 280,983 | ​ | $ | 4.05
Restricted Stock Units [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Schedules of Restricted Stock and Restricted Stock Unit Activity | Certain employees and consultants have been awarded restricted stock units with time-based vesting. The following table summarizes restricted stock units’ activities for the nine months ended September 30, 2021: ​
​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | Weighted Average
​ | ​ | ​ | ​ | Grant Date Fair
​ | ​ | Number of Units | ​ | Value
Nonvested at December 31, 2020 |  | 1,468,559 | ​ | $ | 3.87
Granted |  | 1,100,000 | ​ |  | 3.45
Forfeited | ​ | (298,687) | ​ | ​ | 3.64
Vested |  | (298,690) | ​ |  | 4.29
Nonvested at September 30, 2021 |  | 1,971,182 | ​ | $ | 3.60

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