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Note 7 - Common Stock Options (Tables)
12 Months Ended
Dec. 31, 2021
Notes Tables  
Share-based Payment Arrangement, Option, Activity [Table Text Block]
  

Options

  

Exercise Price

  

Weighted-Average
Exercise Price

 

Options outstanding at December 31, 2018

  5,535,439  

$2.50

-$21.99  $7.30 

Granted

  2,563,500  5.15-19.87   9.36 

Exercised

  (771,376) 2.5-15   4.62 

Forfeitures

  (361,833) 2.50-16.50   7.53 

Options outstanding at December 31, 2019

  6,965,730  

$2.71

-$21.99   6.09 

Granted

  230,500  8.89-21.80   16.85 

Exercised

  (1,784,763) 2.71-19.09   6.08 

Forfeitures

  (84,042) 4.26-21.80   8.55 

Options outstanding at December 31, 2020

  5,327,425  

$2.71

-$21.99   6.09 

Granted

  809,500  

$11.35

-$20.20   13.47 

Exercised

  (1,348,374) 

$3.27

-$15.00   7.78 

Forfeitures

  (131,874) 

$4.14

-$21.99   12.23 

Options outstanding at December 31, 2021

  4,656,677  

$2.71

-$21.74   10.68