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Note 5 - Concentration of Credit Risk (Details Textual)
$ in Thousands
12 Months Ended
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
Cash, FDIC Insured Amount $ 250 $ 250  
Number Of Banks 11 10  
Cash Balances On Deposit FDIC Insured Amount $ 92,800 $ 36,400  
Cash Deposit with Foreign Banks $ 122,500 $ 145,700  
Revenue Benchmark [Member] | Customer Concentration Risk [Member]      
Number of Customers 50 50 50
Concentration Risk, Percentage 3.00%    
Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Top Fifty Customers [Member]      
Concentration Risk, Percentage 33.00% 33.00% 34.00%
Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Individual Customer [Member]      
Number of Customers 0 0 0
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Individual Customer [Member]      
Number of Customers 0 0  
Concentration Risk, Percentage 2.00% 3.00%