Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid research and development project costs	$ 515	$ 878
Prepaid insurance	511	480
Other receivables	70	44
Other	247	271
Total prepaid expenses and other current assets	$ 1,343	$ 1,673