Accrued Liabilities - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities Current [Abstract]
Research and clinical expenses	$ 10,068	$ 3,909
Payroll and related expenses	4,526	3,971
Legal and professional expenses	1,523	264
Property and equipment		331
Other accrued expenses	266	349
Total	$ 16,383	$ 8,824