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Note 4 - Concentration of Credit Risk (Details Textual) - Customer Concentration Risk [Member]
Pure in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Dec. 31, 2021
Revenue from Contract with Customer Benchmark [Member]      
Number of Major Customers 0 0  
Accounts Receivable [Member]      
Number of Major Customers 0   0