Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 44,348	$ 31,713
Less: accumulated depreciation and amortization	(20,911)	(17,755)
Property and equipment, net	23,437	13,958
Prototype
Property Plant And Equipment [Line Items]
Property and equipment, gross	12,512	12,425
Machinery and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	15,588	12,654
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	5,055	4,600
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	998	636
Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,389	1,250
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 8,806	$ 148

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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