Note 4 - Investments (Details Textual) - USD ($)		12 Months Ended
		Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Available-for-sale Equity Securities, Amortized Cost Basis		$ 8,385,000	$ 3,445,000
Available-for-sale Securities, Equity Securities		9,097,000	$ 3,637,000
Percentage of Annual Dividend Return on Investment			3.00%
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		515,000	$ 192,000
AOCI Tax, Attributable to Parent		$ 182,000	68,000
Available-for-sale Securities, Debt Securities, Average Yield		0.40%
Available-for-sale Securities, Debt Securities		$ 7,479,000	0
Capital Gain Distribution from Available for Sale Securities	[1]	39,000	105,000	$ 57,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent		515,000	29,000	(217,000)
Proceeds from Sale of Available-for-sale Securities, Equity		53,000	10,206,000	$ 57,000
Equity Method Investments		58,223,000	57,942,000
EAM Trust [Member]
Equity Method Investments	[2]	$ 58,223,000	57,942,000
Percentage of Non Voting Profit Interest		50.00%
Accrued Non Voting Revenues and Non Voting Profits Interests Payable		$ 1,919,000	1,750,000
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
Fair Value of Contributed Capital at Inception		55,805,000	55,805,000
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		5,000
AOCI Tax, Attributable to Parent		1,000
Equity Securities [Member]
Available-for-sale Securities, Gross Realized Gain (Loss)		0
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent		520,000	29,000
Deferred Taxes on Unrealized Gains on Securities		$ 183,000	9,000
Available-for-sale Securities, Gross Realized Gains			224,000
Debt Securities [Member]
Proceeds from Sale and Maturity of Available-for-sale Securities			$ 0

[1] Capital gain distributions of $39,000, $105,000 and $57,000 were reclassified from Accumulated Other Comprehensive Income in the Consolidated Balance Sheets to the Consolidated Statements of Income in fiscal 2017, 2016 and 2015, respectively.

[2] Reported within Long Term Assets on Consolidated Balance Sheets.