Note 2 - Investments (Details Textual) - USD ($)		6 Months Ended
		Oct. 31, 2016	Oct. 31, 2015	Apr. 30, 2016
EAM Trust [Member]
Fair Value of Contributed Capital at Inception		$ 55,805,000		$ 55,805,000
Cash and Liquid Securities in Excess of Working Capital Requirements Contributed to CapitalAccount		5,820,000		5,820,000
Equity Method Investments	[1]	$ 58,167,000		57,942,000
Percentage of Non Voting Profit Interest		50.00%
Percentage of Non Voting Profits Interests Due from Ex Subsidiary Payable to Parent under Agreement		90.00%
Accrued Non Voting Revenues and Non Voting Profits Interests Payable				1,750,000
Loss From Sale of Equity Securities Reclassified into Consolidated Condensed Statement of Income [Member]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax			$ (15,000)
Equity Securities [Member]
Deferred Taxes on Unrealized Gains on Securities		$ 77,000	19,000
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		2,000
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
AOCI Tax, Attributable to Parent		1,000
Proceeds from Sale of Available-for-sale Securities, Equity		0	8,684,000
Available-for-sale Securities, Debt Securities		6,137,000		0
Available-for-sale Securities, Amortized Cost Basis		8,399,000		3,445,000
Available-for-sale Securities, Equity Securities		8,372,000		3,637,000
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax			15,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent		(218,000)	(40,000)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax		(216,000)	$ (55,000)
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		27,000		192,000
AOCI Tax, Attributable to Parent		$ 9,000		67,000
Available-for-sale Securities, Debt Securities, Average Yield		0.78%
Equity Method Investments		$ 58,167,000		$ 57,942,000
Percentage of Non Voting Profits Interests Due from Ex Subsidiary Payable to Parent under Agreement		90.00%
Accrued Non Voting Revenues and Non Voting Profits Interests Payable		$ 1,918,000

[1] Reported within Long Term Assets on the Consolidated Condensed Balance Sheets.