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Note 8 - Geographic Segment Data - Financial Information by Geographic Area (Details) - USD ($)
 3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Revenue from Contract with Customer, Including Assessed Tax $ 12,536,389 $ 13,979,177  
Sales to outside customers 39,705,058   $ 38,760,834
UNITED STATES      
Revenue from Contract with Customer, Including Assessed Tax 8,760,000 9,738,000  
Sales to outside customers 23,472,000   25,354,000
Europe [Member]      
Revenue from Contract with Customer, Including Assessed Tax 1,275,000 1,362,000  
Sales to outside customers 3,366,000   3,052,000
MEXICO      
Revenue from Contract with Customer, Including Assessed Tax 2,081,000 2,186,000  
Sales to outside customers 11,406,000   9,476,000
UNITED KINGDOM      
Revenue from Contract with Customer, Including Assessed Tax 420,000 $ 693,000  
Sales to outside customers $ 1,461,000   $ 879,000