Balance Sheet Components - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 25,898	$ 23,727
Less: accumulated depreciation and amortization	(14,334)	(12,167)
Property and equipment, net	11,564	11,560
Prototype
Property Plant And Equipment [Line Items]
Property and equipment, gross	11,929	6,405
Machine and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	7,831	6,057
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,438	4,371
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	558	368
Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,142	1,028
Construction In Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 0	$ 5,498

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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.

+ References

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