Note 2 - Investments - Schedule of Carrying Value and Fair Value of Securities Available-for-sale (Details) - USD ($)	Jul. 31, 2017	Apr. 30, 2017
Available-for-sale Equity Securities, Amortized Cost Basis	$ 8,385,000	$ 8,385,000
Available-for-sale Securities, Equity Securities	9,249,000	9,097,000
Fair Value	8,461,000	7,479,000
Amortized Cost	5,626,000	4,384,000
Gross Unrealized Gains		4,000
Gross Unrealized Losses	(5,000)	(3,000)
Fair Value	5,621,000	4,385,000
Amortized Cost	2,850,000	3,100,000
Gross Unrealized Gains
Gross Unrealized Losses	(10,000)	(6,000)
Fair Value	2,840,000	3,094,000
Amortized Cost	8,476,000	7,484,000
Gross Unrealized Gains		4,000
Gross Unrealized Losses	(15,000)	(9,000)
Exchange Traded Funds [Member]
Available-for-sale Equity Securities, Amortized Cost Basis	8,385,000	8,385,000
Gross Unrealized Gains	864,000	712,000
Available-for-sale Securities, Equity Securities	$ 9,249,000	$ 9,097,000