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Note 5 - Sales Concentrations (Details Textual) - Customer Concentration Risk [Member]
9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Revenue Benchmark [Member]    
Number of Major Customers 5 4
Accounts Receivable [Member] | Five Major Customers [Member]    
Concentration Risk, Percentage 75.00%  
Accounts Receivable [Member] | Four Major Customer [Member]    
Concentration Risk, Percentage   66.00%