Note 4 - Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property and equipment, gross	$ 3,342	$ 2,636
Less: accumulated depreciation	(1,825)	(1,570)
Property and equipment, net	1,517	1,066
Laboratory Equipment [Member]
Property and equipment, gross	2,775	2,076
Office Equipment [Member]
Property and equipment, gross	227	227
Leasehold Improvements [Member]
Property and equipment, gross	$ 340	$ 333

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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