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Note 4 - Accounting for Stock-based Compensation (Tables)
 6 Months Ended
Jun. 30, 2020
Notes Tables  
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
   
For Three Months Ended
June 30, 2020
    
For Three Months Ended
June 30, 2019
    
For Six Months
 Ended
June 30, 2020
    
For Six Months
Ended

June 30, 2019
  
                                 
Weighted average grant date fair value
   $
2.80
     $
3.61
     $
2.80
     $
3.61
  
Weighted average assumptions used:
                                
Expected dividend yield
    
0.0
%
    
0.0
%
    
0.0
%
    
0.0
%
Risk-free interest rate
    
0.43
%
    
2.19
%
    
0.43
%
    
2.19
%
Expected volatility
    
76.00
%
    
127.52
%
    
76.00
%
    
127.52
%
Expected life (in years)
    
6.2
      
5.0
      
6.2
      
5.0