Note 2 - Investments (Details Textual) - USD ($)		3 Months Ended		12 Months Ended
		Jul. 31, 2018	Jul. 31, 2017	Apr. 30, 2018
Available-for-sale Equity Securities, Amortized Cost Basis, Total		$ 8,385,000		$ 8,385,000
Available-for-sale Securities, Equity Securities		9,917,000		$ 9,379,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent, Total		539,000	$ 142,000
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax		$ 113,000	50,000
Available-for-sale Securities, Debt Securities, Average Yield		1.70%		1.24%
Equity Method Investments		$ 58,331,000		$ 58,233,000
EAM Trust [Member]
Equity Method Investments	[1]	58,331,000		58,233,000
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%
Accrued Non Voting Revenues and Non Voting Profits Interests Payable		$ 2,279,000		2,113,000
Equity Securities [Member]
Available-for-sale Securities, Gross Realized Gain (Loss), Total		0	0
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent, Total		538,000	152,000
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax		113,000	54,000
Accumulated Other Comprehensive Income (Loss), Debt Securities, Available-for-sale, Adjustment, after Tax, Ending Balance		1,532,000	994,000
AOCI Tax, Attributable to Parent		322,000	209,000
Debt Securities [Member]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent, Total		(2,000)	10,000
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax		(1,000)	4,000
Accumulated Other Comprehensive Income (Loss), Debt Securities, Available-for-sale, Adjustment, after Tax, Ending Balance		(1,000)		(3,000)
AOCI Tax, Attributable to Parent		(200)		$ (600)
Proceeds from Sale and Maturity of Debt Securities, Available-for-sale, Total		$ 1,637,000	$ 1,394,000

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