Stockholders' Equity - Stock-based compensation expense (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2019 |
Sep. 30, 2018 |
Sep. 30, 2019 |
Sep. 30, 2018 |
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| Share-based Compensation | $ 1,120 | $ 903 | $ 2,174 | $ 3,869 |
| General and administrative [Member] | ||||
| Share-based Compensation | 389 | 201 | 1,058 | 1,137 |
| Research and development [Member] | ||||
| Share-based Compensation | $ 731 | $ 702 | $ 1,116 | $ 2,732 |
| X | ||||||||||
- Definition Amount of noncash expense for share-based payment arrangement. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Details
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| X | ||||||||||
- Details
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