Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 26,582	$ 23,142
Less: accumulated depreciation and amortization	(16,159)	(13,169)
Property and equipment, net	10,423	9,973
Machinery and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 15,244	13,268
Machinery and Equipment | Minimum
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful lives	2 years
Machinery and Equipment | Maximum
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful lives	3 years
Production Masks
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful lives	4 years
Property and equipment, gross	$ 5,401	5,401
Software and Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful lives	3 years
Property and equipment, gross	$ 4,223	3,820
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful lives	Shorter of estimated life of asset or remaining lease term
Property and equipment, gross	$ 1,546	539
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful lives	3 years
Property and equipment, gross	$ 168	$ 114