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Note 1 - Description of Business and Summary of Significant Accounting Policies (Tables)
6 Months Ended
Jun. 30, 2021
Notes Tables  
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]
  

Three Months Ended June 30,

  

Six Months Ended June 30,

 
  

2021

  

2020

  

2021

  

2020

 

Stock options

  406,960   1,922,935   299,743   1,748,717 

Restricted stock units

     39,152   84,527   57,806