Selected Balance Sheet Components - Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and equipment, net:
Total property and equipment, gross	$ 13,411	$ 10,692
Accumulated depreciation	(7,505)	(6,621)
Property and Equipment	5,906	4,071
Depreciation expense	1,400	1,600	$ 1,600
Machinery and equipment
Property and equipment, net:
Total property and equipment, gross	1,536	1,249
Furniture, fixtures and office equipment
Property and equipment, net:
Total property and equipment, gross	775	872
Computer equipment and software
Property and equipment, net:
Total property and equipment, gross	3,712	3,536
Leasehold improvements
Property and equipment, net:
Total property and equipment, gross	4,587	4,213
Construction in process
Property and equipment, net:
Total property and equipment, gross	$ 2,801	$ 822

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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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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