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Note 8 - Segment and Geographic Information - Customers with Sales and Accounts Receivable Greater Than 10% (Details) - Customer Concentration Risk [Member]
3 Months Ended 12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Revenue Benchmark [Member] | Distributor A [Member]      
Concentration risk 23.00% 20.00%  
Revenue Benchmark [Member] | Distributor B [Member]      
Concentration risk [1] 10.00%  
Accounts Receivable [Member] | Distributor A [Member]      
Concentration risk 22.00%   25.00%
Accounts Receivable [Member] | Distributor B [Member]      
Concentration risk 17.00%   16.00%
[1] Represents less than 10%.