Stock Based Compensation (Details) - USD ($) $ in Thousands  | 
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2017  | 
Jun. 30, 2016  | 
Jun. 30, 2017  | 
Jun. 30, 2016  | 
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| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||||
| Allocated Share-based Compensation Expense | $ 316 | $ 401 | $ 1,688 | $ 794 | 
| Research and development | ||||
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||||
| Allocated Share-based Compensation Expense | 70 | 140 | 505 | 271 | 
| General and administrative | ||||
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||||
| Allocated Share-based Compensation Expense | $ 246 | $ 261 | $ 1,183 | $ 523 | 
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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://www.xbrl.org/2003/role/presentationRef 
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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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