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Note 14 - Copyright Fees (Details Textual) - USD ($)
 12 Months Ended
Apr. 30, 2021
Apr. 30, 2020
Apr. 30, 2019
Revenue from Contract with Customer, Including Assessed Tax $ 40,392,000 $ 40,299,000 $ 36,257,000
Percentage of Copyright Data Fees   70.40%  
Third Party Sponsored Assets for Copyright Data 11,600,000,000 $ 8,600,000,000  
License [Member]      
Revenue from Contract with Customer, Including Assessed Tax $ 12,763,000 $ 12,671,000 $ 7,437,000
Percentage of Copyright Data Fees 0.70%