Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 33,916	$ 31,713
Less: accumulated depreciation and amortization	(18,637)	(17,755)
Property and equipment, net	15,279	13,958
Prototype
Property Plant And Equipment [Line Items]
Property and equipment, gross	12,247	12,425
Machinery and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	13,871	12,654
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,621	4,600
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	665	636
Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,296	1,250
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,216	$ 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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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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