Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid research and development project costs	$ 184	$ 878
Prepaid insurance	774	480
Other receivables	453	44
Other	411	271
Total prepaid expenses and other current assets	$ 1,822	$ 1,673