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Note 12 - Summary of Stock Options - Valuation Assumptions for Stock Options (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Expected term (Year) 6 years 5 years
Average volatility 70.00% 73.00%
Risk-free interest rate 1.62% 2.65%
Dividend yield 0.00% 0.00%
Nonemployees [Member]    
Expected term (Year) 6 years 9 years
Average volatility 70.00% 69.00%
Risk-free interest rate 1.69% 2.69%
Dividend yield 0.00% 0.00%