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Note 9 - Concentration of Credit Risk (Details Textual) - Customer Concentration Risk [Member]
3 Months Ended 6 Months Ended
Jun. 30, 2019
USD ($)
Jun. 30, 2018
USD ($)
Jun. 30, 2019
USD ($)
Jun. 30, 2018
USD ($)
Revenue Benchmark [Member]        
Number of Major Customers 2 2 2 2
Revenue Benchmark [Member] | Customer One [Member]        
Concentration Risk, Percentage 34.00% 30.00% 25.00% 24.00%
Revenue Benchmark [Member] | Customer Two [Member]        
Concentration Risk, Percentage 22.00% 23.00% 27.00% 27.00%
Accounts Receivable [Member] | Customer One [Member]        
Accounts Receivable, before Allowance for Credit Loss $ 2,488,000 $ 4,808,000 $ 2,488,000 $ 4,808,000
Concentration Risk, Percentage     30.00% 57.00%
Accounts Receivable [Member] | Customer Two [Member]        
Accounts Receivable, before Allowance for Credit Loss $ 1,044,000 $ 1,524,000 $ 1,044,000 $ 1,524,000
Concentration Risk, Percentage     12.00% 18.00%