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Grant Revenue - Additional Information (Details) - USD ($)
$ in Thousands
1 Months Ended 3 Months Ended 9 Months Ended
Feb. 28, 2018
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Disaggregation Of Revenue [Line Items]          
Revenue   $ 411   $ 411  
Type of Revenue [Extensible List]   us-gaap:GrantMember us-gaap:GrantMember us-gaap:GrantMember us-gaap:GrantMember
SBIR Grants          
Disaggregation Of Revenue [Line Items]          
Revenue   $ 400   $ 400  
Grants from the National Institutes of Health $ 2,800        
Type of Revenue [Extensible List]   us-gaap:GrantMember   us-gaap:GrantMember