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Note 3 - Concentration of Credit Risk (Details Textual)
3 Months Ended 6 Months Ended
Jun. 30, 2018
USD ($)
Jun. 30, 2017
Jun. 30, 2018
USD ($)
Jun. 30, 2017
Dec. 31, 2017
USD ($)
Cash, Uninsured Amount $ 14,280,000   $ 14,280,000   $ 12,198,000
Export Sales To Unaffiliated Customers As Percentage Of Total Sales 10.00%        
Number Of Major Customers 1 1      
Accounts Receivable [Member]          
Number Of Major Customers     3    
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Customer A [Member]          
Concentration Risk, Percentage 37.00% 66.00% 43.00% 68.00%