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Note 14 - Concentration (Details Textual) - USD ($)
3 Months Ended
Jul. 31, 2020
Jul. 31, 2019
Revenue from Contract with Customer, Including Assessed Tax $ 10,328,000 $ 9,617,000
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | One Single Customer [Member]    
Concentration Risk, Percentage 31.30%  
Revenue from Contract with Customer, Including Assessed Tax $ 10,328,000