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 9 Months Ended
Sep. 30, 2018
Jun. 30, 2018
Sep. 30, 2017
Jun. 30, 2018
Sep. 30, 2018
Sep. 30, 2017
Expected term (Year) 5 years   5 years   5 years 5 years
Average volatility 70.00%   64.00%   73.00% 55.00%
Risk-free interest rate 2.86%   1.73%   2.67% 1.83%
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   67.00%   67.00%    
Risk-free interest rate   1.93%   1.71%    
Dividend yield   0.00%   0.00%