Balance Sheet Components - Property and Equipment Net (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Property and Equipment, Net
Total property and equipment, gross	$ 14,765	$ 13,322
Less: accumulated depreciation	(10,479)	(9,376)
Total property and equipment, net	4,286	3,946
Depreciation and amortization expense	1,500	1,200
Manufacturing equipment
Property and Equipment, Net
Total property and equipment, gross	11,723	10,465
Computer and network equipment
Property and Equipment, Net
Total property and equipment, gross	820	710
Furniture and fixtures
Property and Equipment, Net
Total property and equipment, gross	110	218
Software
Property and Equipment, Net
Total property and equipment, gross	680	455
Leasehold improvements
Property and Equipment, Net
Total property and equipment, gross	$ 1,432	$ 1,474

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 of expense for allocation of cost of tangible and intangible assets over their useful lives directly used in production of good and rendering of service.

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