Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities And Other Liabilities [Abstract]
Accrued compensation	$ 1,837	$ 1,270
Accrued contracted research and development costs	2,552	1,749
Accrued professional and consulting fees	672	480
Accrued and other current liabilities	159	227
Total accrued and other current liabilities	$ 5,220	$ 3,726