Balance Sheets Components (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued personnel expenses	$ 470	$ 1,108
Accrued clinical and development expenses	2,506	2,250
Other	198	201
Total	$ 3,174	$ 3,559