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Note 10 - Concentration of Credit Risk (Tables)
3 Months Ended
Mar. 31, 2020
Notes Tables  
Schedules of Concentration of Risk, by Risk Factor [Table Text Block]
   
Three Months Ended
   
Three Months Ended
 
   
March 31, 2020
   
March 31, 2019
 
Customer
 
Net Sales
   
% of Net Sales
   
Net Sales
   
% of Net Sales
 
Customer A
  $
3,222,000
     
45
%   $
3,861,000
     
45
%