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Note 7 - Segment Information - Net Sales for Geographic Areas (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Net sales $ 19,177,767 $ 19,280,770 $ 39,466,685 $ 39,430,615
UNITED STATES        
Net sales 16,361,760 16,546,075 33,709,933 33,828,738
CANADA        
Net sales 1,619,430 1,646,224 3,362,604 3,419,734
All Other Countries [Member]        
Net sales $ 1,196,577 $ 1,088,471 $ 2,394,148 $ 2,182,143