Note 13 - Equity Incentive Plans - Total Stock-based Compensation Recognized for Options (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Stock-based compensation	$ 627	$ 539
Research and Development Expense [Member]
Stock-based compensation	253	254
General and Administrative Expense [Member]
Stock-based compensation	$ 374	$ 285

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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