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Note 17 - Segment Data (Details Textual)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Number of Reportable Segments 1    
Number of Operating Segments 1    
Customer Concentration Risk [Member] | Revenue Benchmark [Member]      
Number of Major Customers 0 0 0
Customer Concentration Risk [Member] | Accounts Receivable [Member]      
Number of Major Customers 1 1  
Customer Concentration Risk [Member] | Accounts Receivable [Member] | One Customer [Member]      
Concentration Risk, Percentage 13.30% 13.90%