Stockholders' Equity - Stock-based compensation expense (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2019 |
Jun. 30, 2018 |
Jun. 30, 2019 |
Jun. 30, 2018 |
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| Share-based Compensation | $ 622 | $ 971 | $ 1,054 | $ 2,966 |
| General and Administrative Expense | ||||
| Share-based Compensation | 333 | 393 | 669 | 936 |
| Research and Development Expense | ||||
| Share-based Compensation | $ 289 | $ 578 | $ 385 | $ 2,030 |
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- Definition The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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