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Note 2 - Revenue - Concentration of Revenue (Details) - Revenue Benchmark [Member] - Customer Concentration Risk [Member]
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Customer A [Member]        
Concentration 72.00% 68.00% 71.00% 67.00%
Customer B [Member]        
Concentration 5.00% 11.00% 6.00% 11.00%