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Note 1 - Organization and Summary of Significant Accounting Policies - Schedule of Fair Value Measurements of Investments (Details) - USD ($)
Apr. 30, 2023
Apr. 30, 2022
Cash equivalents $ 7,240,000 $ 28,965,000
Equity Securities, FV-NI 14,546,000 17,647,000
Available-for-sale fixed income securities 39,928,000 10,475,000
Investments, Fair Value Disclosure 61,714,000 57,087,000
Fair Value, Inputs, Level 1 [Member]    
Cash equivalents 7,240,000 28,965,000
Equity Securities, FV-NI 14,546,000 17,647,000
Available-for-sale fixed income securities 39,928,000 10,475,000
Investments, Fair Value Disclosure 61,714,000 57,087,000
Fair Value, Inputs, Level 2 [Member]    
Cash equivalents 0 0
Equity Securities, FV-NI 0 0
Available-for-sale fixed income securities 0 0
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member]    
Cash equivalents 0 0
Equity Securities, FV-NI 0 0
Available-for-sale fixed income securities 0 0
Investments, Fair Value Disclosure $ 0 $ 0