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Stock-based Compensation (Tables) | 9 Months Ended
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Sep. 30, 2021
Stock-based Compensation |
Weighted Average Assumptions | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended September 30, |  | ​ | Nine Months Ended September 30, |
​ |  | 2021 |  | 2020 (1) |  |  | 2021 |  | 2020 |
Dividend yield |  | 0 | % | n/a | ​ |  | 0 | % | 0 | %
Expected volatility |  | 71 | % | n/a | ​ |  | 90 | % | 100 | %
Risk-free interest rate |  | 0.85 | % | n/a | ​ |  | 0.79 | % | 0.77 | %
Expected term |  | 5.61 years | ​ | n/a | ​ |  | 5.67 years | ​ | 5.66 years | ​
Stock Option Activity | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted |  | Weighted |  | ​
​ | ​ | ​ | ​ | Average | ​ | Average | ​ | Aggregate
​ | ​ | ​ | ​ | Exercise | ​ | Contractual | ​ | Intrinsic
​ | ​ | Number of | ​ | Price | ​ | Term | ​ | Value
​ | ​ | shares | ​ | Per Share | ​ | (in years) | ​ | (in thousands)
Outstanding at January 1, 2021 | ​ | ​ | 1,827,906 | ​ | $ | 20.66 |  | ​ | 6.31 |  | $ | 51,401
Granted |  | ​ | 213,711 | ​ |  | 36.32 |  | ​ |  |  | ​ |
Exercised |  | ​ | (74,805) | ​ |  | 13.54 |  | ​ |  |  | ​ |
Forfeited, expired or cancelled | ​ | ​ | (57,115) | ​ |  | 71.26 |  | ​ |  |  | ​ |
Outstanding at September 30, 2021 | ​ | ​ | 1,909,697 | ​ | $ | 21.18 |  | ​ | 6.02 | ​ | $ | 20,077
Exercisable at September 30, 2021 | ​ | ​ | 1,595,665 | ​ | $ | 19.53 |  | ​ | 5.45 | ​ | $ | 19,276
Stock-based Compensation Expense | The following table shows total stock-based compensation expense for stock options and ESPP in the condensed consolidated statements of operations and comprehensive loss (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended September 30, | ​ | Nine Months Ended September 30,
​ |  | 2021 |  | 2020 |  | 2021 |  | 2020
Research and development | ​ | $ | — | ​ | $ | — | ​ | $ | — | ​ | $ | —
General and administrative | ​ |  | 779 | ​ |  | 708 | ​ |  | 4,445 | ​ |  | 3,269
Total stock-based compensation expense | ​ | $ | 779 | ​ | $ | 708 | ​ | $ | 4,445 | ​ | $ | 3,269

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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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