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Note 4 - Investments - Schedule of Carrying Value and Fair Value of Equity Securities (Details) - USD ($)
Apr. 30, 2021
Apr. 30, 2020
May 01, 2018
Equity securities, cost $ 19,105,000 $ 12,877,000  
Equity securities, gross unrealized gains     $ 994,000
Equity securities, fair value 23,582,000 14,125,000 $ 9,379,000
Exchange Traded Funds [Member]      
Equity securities, cost 19,105,000 12,877,000  
Equity securities, gross unrealized gains 4,532,000 1,317,000  
Equity securities, gross unrealized losses (55,000) (69,000)  
Equity securities, fair value $ 23,582,000 $ 14,125,000