Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid research and development project costs	$ 878	$ 515
Prepaid insurance	480	23
Other	315	23
Total prepaid expenses and other current assets	$ 1,673	$ 561