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Note 9 - Stockholders' Equity - Summary of Option Activity for Employees and Non-employees (Details) - Share-based Payment Arrangement, Option [Member] - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Dec. 31, 2019
Share-based Payment Arrangement, Employee [Member]        
Number of options (in shares) 1,953,443 1,212,442 1,212,442  
Weighted average exercise price, outstanding (in dollars per share) $ 1.88 $ 1.71 $ 1.71  
Weighted average remaining contractual life, outstanding (Year) 3 years 226 days 2 years 146 days 3 years 32 days 2 years 146 days
Aggregate intrinsic value, outstanding $ 2,457,153 $ 476,964
Number of options granted (in shares) 32,175    
Weighted average exercise price, granted (in dollars per share) $ 3.11    
Weighted average remaining contractual life, granted (Year)    
Aggregate intrinsic value, granted    
Number of options exercised (in shares)    
Weighted average exercise price, exercised (in dollars per share)    
Weighted average remaining contractual life, exercised (Year)    
Aggregate intrinsic value, exercised    
Number of options forfeited and expired (in shares) (435,558)    
Weighted average exercise price, forfeited or expired (in dollars per share) $ 1.58    
Number of options exercisable (in shares) 745,045 1,117,829    
Weighted average exercise price, exercisable (in dollars per share) $ 1.93 $ 1.84    
Weighted average remaining contractual life, exercisable (Year) 2 years 219 days 1 year 306 days    
Aggregate intrinsic value, exercisable $ 1,222,127    
Number of options (in shares) 1,550,060 1,212,442 1,953,443 1,212,442
Weighted average exercise price, outstanding (in dollars per share) $ 1.98 $ 1.71 $ 1.88 $ 1.71
Number of options exercised (in shares)    
Share-based Payment Arrangement, Nonemployee [Member]        
Number of options (in shares) 74,997 49,998 49,998  
Weighted average exercise price, outstanding (in dollars per share) $ 1.41 $ 1.87 $ 1.87  
Weighted average remaining contractual life, outstanding (Year) 3 years 109 days 2 years 343 days 3 years 65 days 2 years 343 days
Aggregate intrinsic value, outstanding $ 161,660 $ 54,748
Number of options granted (in shares) 16,666 8,333    
Weighted average exercise price, granted (in dollars per share) $ 4.30 $ 1.65    
Weighted average remaining contractual life, granted (Year)    
Aggregate intrinsic value, granted    
Number of options exercised (in shares)    
Weighted average exercise price, exercised (in dollars per share)    
Number of options exercisable (in shares) 52,769 41,663    
Weighted average exercise price, exercisable (in dollars per share) $ 1.34 $ 1.71    
Weighted average remaining contractual life, exercisable (Year) 2 years 135 days 2 years 10 days    
Aggregate intrinsic value, exercisable $ 117,829 $ 84,579    
Number of options (in shares) 91,663 58,331 74,997 49,998
Weighted average exercise price, outstanding (in dollars per share) $ 1.87 $ 1.87 $ 1.41 $ 1.87
Number of options exercised (in shares)