Quarterly report pursuant to Section 13 or 15(d)

Note 11 - Summary of Stock Options - Summary of Option Activity Under All Plans (Details)

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Note 11 - Summary of Stock Options - Summary of Option Activity Under All Plans (Details) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Options outstanding, beginning of period (in shares) 10,087,678  
Options outstanding, weighted average exercise price (in dollars per share) $ 2.22  
Options outstanding, weighted average remaining contractual term (Year) 9 years 255 days 9 years 328 days
Options outstanding, aggregate intrinsic value $ 3,928,715
Options granted (in shares) 468,000  
Options granted, weighted average exercise price (in dollars per share) $ 0.88  
Options exercised (in shares)  
Options exercised, weighted average exercise price (in dollars per share)  
Options canceled (in shares) (123,024)  
Options canceled, weighted average exercise price (in dollars per share) $ 20.25  
Options outstanding, end of period (in shares) 10,432,654 10,087,678
Options outstanding, weighted average exercise price (in dollars per share) $ 1.95 $ 2.22
Vested and exercisable and expected to vest, end of period (in shares) 9,404,561  
Vested and exercisable and expected to vest, end of period, weighted average exercise price (in dollars per share) $ 2.04  
Vested and exercisable and expected to vest, end of period, weighted average remaining contractual term (Year) 9 years 255 days  
Vested and exercisable and expected to vest, end of period, aggregate intrinsic value  
Vested and exercisable, end of period (in shares) 833,785  
Vested and exercisable, end of period, weighted average exercise price (in dollars per share) $ 9.63  
Vested and exercisable, end of period, weighted average remaining contractual term (Year) 9 years 219 days  
Vested and exercisable, end of period, aggregate intrinsic value