Balance Sheet Components - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 32,828	$ 23,216
Less accumulated depreciation	(10,991)	(6,161)
Property and equipment, net	21,837	17,055
Research and Development Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	7,696	2,154
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,873	2,595
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,563	2,013
Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,182	3,931
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	15,085	12,486
Construction-in-progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 429	$ 37