Note 3 - Related Party Transactions - Non-voting Revenues Interest and Non-voting Profits Interests (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Non-voting revenues interest in EAM	$ 11,184	$ 8,260	$ 8,040
Non-voting profits interest in EAM	1,166	1,049	746
Revenues and Profits Distribution from Unconsolidated Entity	$ 12,350	$ 9,309	$ 8,786