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Note 7 - Segment Reporting (Details Textual)
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Number of Reportable Segments 2  
Geographic Concentration Risk [Member] | Revenue Benchmark [Member] | UNITED STATES    
Concentration Risk, Percentage 83.00% 77.00%
Geographic Concentration Risk [Member] | Net Assets, Geographic Area [Member] | UNITED STATES    
Concentration Risk, Percentage 82.00% 81.00%