Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid research and development project costs	$ 33	$ 878
Prepaid insurance	84	480
Other receivables	154	44
Other	272	271
Total prepaid expenses and other current assets	$ 543	$ 1,673