Quarterly report pursuant to Section 13 or 15(d)

Note 9 - Summary of Stock Options - Valuation Assumption for Employee Stock Purchase Plan (Details)

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Note 9 - Summary of Stock Options - Valuation Assumption for Employee Stock Purchase Plan (Details)
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Expected term (Year) 5 years 5 years 5 years 5 years
Average volatility 69.00% 48.00% 75.00% 48.00%
Risk-free interest rate 2.82% 1.76% 2.63% 1.90%
Dividend yield 0.00% 0.00% 0.00% 0.00%
2017 Employee Stock Purchase Plan [Member]        
Expected term (Year) 91 days   91 days  
Average volatility 74.00%   67.00%  
Risk-free interest rate 1.73%   1.58%  
Dividend yield 0.00%   0.00%