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Note 8 - Share-based Compensation - Unvested Balance of Options (Details) - $ / shares
 9 Months Ended 12 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Unvested, number of options (in shares) 1,225,000  
Unvested, weighted average exercise price per share (in dollars per share) $ 3.93  
Unvested, weighted average remaining contractual term (Year) 7 years 7 months 6 days 8 years 4 months 24 days
Granted, number of options (in shares) 108,000  
Granted, weighted average exercise price per share (in dollars per share) $ 6.33  
Granted, weighted average remaining contractual term (Year) 9 years 8 months 12 days  
Vested, number of options (in shares) (436,000)  
Vested, weighted average exercise price per share (in dollars per share)  
Unvested, number of options (in shares) 897,000 1,225,000
Unvested, weighted average exercise price per share (in dollars per share) $ 4.91 $ 3.93