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Note 4 - Accounting for Stock-based Compensation (Tables)
 6 Months Ended
Jun. 30, 2019
Notes Tables  
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
   
For Three
Months Ended
June 30, 201
9
    
For Three
Months Ended
June 30, 2018
    
For Six
Months Ended
June 30, 201
9
    
For Six
Months Ended

June 30, 201
8
  
                                 
Weighted average grant date fair value
   $
3.61
     $
0.99
     $
3.61
     $
0.99
  
Weighted average assumptions used:
                                
Expected dividend yield
    
0.0
%
    
0.0
%
    
0.0
%
    
0.0
%
Risk-free interest rate
    
2.19
%
    
2.93
%
    
2.19
%
    
2.93
%
Expected volatility
    
127.52
%
    
131.0
%
    
127.52
%
    
131.0
%
Expected life (in years)
    
5.0
      
5.0
      
5.0
      
5.0