Note 1 - Organization and Summary of Significant Accounting Policies - Schedule of Fair Value Measurements of Investments (Details) - USD ($)	Oct. 31, 2023	Apr. 30, 2023
Cash equivalents	$ 3,427,000	$ 7,240,000
Equity Securities, FV-NI	13,064,000	14,546,000
Available-for-sale fixed income securities	42,906,000	39,928,000
Investments, Fair Value Disclosure	59,397,000	61,714,000
Fair Value, Inputs, Level 1 [Member]
Cash equivalents	3,427,000	7,240,000
Equity Securities, FV-NI	13,064,000	14,546,000
Available-for-sale fixed income securities	42,406,000	39,178,000
Investments, Fair Value Disclosure	58,897,000	60,964,000
Fair Value, Inputs, Level 2 [Member]
Cash equivalents	0	0
Equity Securities, FV-NI	0	0
Available-for-sale fixed income securities	500,000	750,000
Investments, Fair Value Disclosure	500,000	750,000
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