Balance Sheet Components - Summary of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Abstract]
Cash	$ 778	$ 1,964
Cash equivalents:
Money market accounts	107,046	107,043
Total cash and cash equivalents	$ 107,824	$ 109,007	$ 122,682	$ 150,180