Note 4 - Investments (Details Textual) - USD ($)		9 Months Ended	12 Months Ended
		Jan. 31, 2017	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Available-for-sale Equity Securities, Amortized Cost Basis, Total			$ 8,385,000	$ 8,385,000
Available-for-sale Securities, Equity Securities			9,379,000	9,097,000
Proceeds from Sale of Available-for-sale Securities, Equity			152,000	53,000	$ 10,206,000
Capital Gain Distribution from Available for Sale Securities	[1]		152,000	39,000	105,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent, Total			285,000	515,000	29,000
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax			$ (8,000)	$ 196,000	126,000
Available-for-sale Securities, Debt Securities, Average Yield			1.24%	0.69%
Available-for-sale Securities, Gross Realized Gains					$ 224,000
Accumulated Other Comprehensive Income (Loss), Debt Securities, Available-for-sale, Adjustment, after Tax, Ending Balance			$ 285,000	$ 515,000
AOCI Tax, Attributable to Parent			40,000	182,000
Equity Method Investments			58,233,000	58,223,000
EAM Trust [Member]
Equity Method Investments	[2]		58,233,000	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%
Accrued Non Voting Revenues and Non Voting Profits Interests Payable			$ 2,113,000	1,919,000
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			282,000	520,000
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax			42,000	183,000
Debt Securities [Member]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent, Total			(2,500)	(5,000)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax			$ (1,200)	$ (1,000)

[1] Capital gain distributions of $152,000, $39,000 and $105,000 were reclassified from Accumulated Other Comprehensive Income in the Consolidated Balance Sheets to the Consolidated Statements of Income in fiscal 2018, 2017 and 2016, respectively.

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