Note 1 - Organization and Summary of Significant Accounting Policies - Schedule of Fair Value Measurements of Investments (Details) - USD ($)	Jul. 31, 2022	Apr. 30, 2022
Cash equivalents	$ 14,033,000	$ 28,965,000
Equity Securities, FV-NI, Total	17,696,000	17,647,000
Available-for-sale fixed income securities	26,032,000	10,475,000
Investments, Fair Value Disclosure, Total	57,761,000	57,087,000
Fair Value, Inputs, Level 1 [Member]
Cash equivalents	14,033,000	28,965,000
Equity Securities, FV-NI, Total	17,696,000	17,647,000
Available-for-sale fixed income securities	26,032,000	10,475,000
Investments, Fair Value Disclosure, Total	57,761,000	57,087,000
Fair Value, Inputs, Level 2 [Member]
Cash equivalents	0	0
Equity Securities, FV-NI, Total	0	0
Available-for-sale fixed income securities	0	0
Investments, Fair Value Disclosure, Total	0	0
Fair Value, Inputs, Level 3 [Member]
Cash equivalents	0	0
Equity Securities, FV-NI, Total	0	0
Available-for-sale fixed income securities	0	0
Investments, Fair Value Disclosure, Total	$ 0	$ 0