Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other receivables	$ 1,487	$ 751
Prepaid research and development project costs	1,050	762
Prepaid insurance	371	555
Income taxes receivable	138	163
Other	653	475
Total prepaid expenses and other current assets	$ 3,699	$ 2,706