Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands |
3 Months Ended | |
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Mar. 31, 2019 |
Mar. 31, 2018 |
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| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||
| Total stock-based compensation expense | $ 1,728 | $ 1,416 |
| Research and Development [Member] | ||
| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||
| Total stock-based compensation expense | 49 | 104 |
| General and Administrative [Member] | ||
| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||
| Total stock-based compensation expense | $ 1,679 | $ 1,312 |
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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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