Note 2 - Investments (Details Textual) - USD ($)		3 Months Ended		12 Months Ended
		Jul. 31, 2017	Jul. 31, 2016	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
Proceeds from Sale of Available-for-sale Securities, Equity		0	$ 0
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		864,000		712,000
AOCI Tax, Attributable to Parent		304,000		$ 251,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent		$ 142,000	238,000
Available-for-sale Securities, Debt Securities, Average Yield		0.97%		0.69%
Equity Method Investments		$ 58,454,000		$ 58,223,000
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		$ 2,119,000
EAM Trust [Member]
Equity Method Investments	[1]	58,454,000		58,223,000
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 Investment, Other than Temporary Impairment		$ 0		$ 0
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%		90.00%
Accrued Non Voting Revenues and Non Voting Profits Interests Payable		$ 2,119,000		$ 1,919,000
Equity Securities [Member]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent		152,000	238,000
Deferred Taxes on Unrealized Gains on Securities		54,000	84,000
Debt Securities [Member]
Proceeds from Sale and Maturity of Available-for-sale Securities		1,394,000		$ 0
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent		(15,000)	5,000
Deferred Taxes on Unrealized Gains on Securities		$ 5,000	$ 1,000

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