Balance Sheet Components - Property and Equipment Net (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Property and Equipment, Net
Total property and equipment, gross	$ 15,694	$ 15,586
Less: accumulated depreciation	(13,748)	(12,107)
Total property and equipment, net	1,946	3,479
Depreciation and amortization expense	2,000	1,700
Manufacturing equipment
Property and Equipment, Net
Total property and equipment, gross	12,296	12,228
Computer and network equipment
Property and Equipment, Net
Total property and equipment, gross	917	877
Furniture and fixtures
Property and Equipment, Net
Total property and equipment, gross	112	112
Software
Property and Equipment, Net
Total property and equipment, gross	925	925
Leasehold improvements
Property and Equipment, Net
Total property and equipment, gross	$ 1,444	$ 1,444

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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