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Note 10 - Concentration of Credit Risk (Details Textual) - Customer Concentration Risk [Member]
3 Months Ended
Mar. 31, 2021
USD ($)
Mar. 31, 2020
USD ($)
Revenue Benchmark [Member]    
Number of Major Customers 1 1
Revenue Benchmark [Member] | Customer One [Member]    
Concentration Risk, Percentage 54.00% 46.00%
Accounts Receivable [Member] | Customer One [Member]    
Accounts Receivable, before Allowance for Credit Loss $ 2,385,000 $ 2,097,000
Concentration Risk, Percentage 33.00% 29.00%