Note 11 - Equity Incentive Plans - Total Stock-based Compensation Recognized for Options (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Stock-based compensation	$ 146	$ 183	$ 490	$ 387
Research and Development Expense [Member]
Stock-based compensation	63	92	222	195
General and Administrative Expense [Member]
Stock-based compensation	$ 83	$ 91	$ 268	$ 192

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

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