Note 1 - Organization and Summary of Significant Accounting Policies - Schedule of Fair Value Measurements of Investments (Details) - USD ($)	Jan. 31, 2024	Apr. 30, 2023
Cash equivalents	$ 4,739,000	$ 7,240,000
Equity Securities, FV-NI	15,370,000	14,546,000
Available-for-sale fixed income securities	46,149,000	39,928,000
Investments, Fair Value Disclosure	66,258,000	61,714,000
Fair Value, Inputs, Level 1 [Member]
Cash equivalents	4,739,000	7,240,000
Equity Securities, FV-NI	15,370,000	14,546,000
Available-for-sale fixed income securities	45,899,000	39,178,000
Investments, Fair Value Disclosure	66,008,000	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	250,000	750,000
Investments, Fair Value Disclosure	250,000	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