| Stock Based Compensation (Details) - USD ($) $ in Thousands | 3 Months Ended | |
|---|---|---|
| Mar. 31, 2017 | Mar. 31, 2016 | |
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||
| Allocated Share-based Compensation Expense | $ 1,372 | $ 393 | 
| Research and development | ||
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||
| Allocated Share-based Compensation Expense | 435 | 131 | 
| General and administrative | ||
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||
| Allocated Share-based Compensation Expense | $ 937 | $ 262 | 
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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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