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Note 16 - Concentration (Details Textual) - USD ($)
12 Months Ended
Apr. 30, 2023
Apr. 30, 2022
Apr. 30, 2021
Revenue from Contract with Customer, Including Assessed Tax $ 39,695,000 $ 40,525,000 $ 40,392,000
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | One Single Customer [Member]      
Concentration Risk, Percentage 33.90% 33.00% 31.60%
Revenue from Contract with Customer, Including Assessed Tax $ 39,695,000 $ 40,525,000 $ 40,392,000