Balance Sheet Components - Schedule of Deferred Revenue (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Deferred Revenue [Line Items]
Total deferred revenue	$ 16,521	$ 23,389
Less: current portion of deferred revenue	(11,315)	(20,151)
Noncurrent portion of deferred revenue	5,206	3,238
Product
Deferred Revenue [Line Items]
Total deferred revenue	7,478	18,861
Service
Deferred Revenue [Line Items]
Total deferred revenue	6,053	1,182
Distribution Rights
Deferred Revenue [Line Items]
Total deferred revenue	$ 2,990	$ 3,346