Note 2 - Investments (Details Textual) - USD ($)	9 Months Ended		12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Apr. 30, 2019
Available-for-sale Equity Securities, Amortized Cost Basis, Total	$ 10,257,000		$ 8,541,000
Available-for-sale Securities, Equity Securities	12,861,000		$ 10,622,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent, Total	592,000	$ 438,000
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	$ 260,000	93,000
Available-for-sale Securities, Debt Securities, Average Yield	2.30%		2.09%
Equity Method Investments	$ 59,612,000		$ 58,625,000
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 Capital Account	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	$ 3,413,000		2,420,000
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	523,000	404,000
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	240,000	85,000
AOCI, Debt Securities, Available-for-sale, Adjustment, after Tax, Total	2,604,000		2,081,000
AOCI Tax, Attributable to Parent	677,000		437,000
Debt Securities [Member]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent, Total	69,000	34,000
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	20,000	8,000
AOCI, Debt Securities, Available-for-sale, Adjustment, after Tax, Total	112,000		43,000
AOCI Tax, Attributable to Parent	29,000		$ 9,000
Proceeds from Sale and Maturity of Debt Securities, Available-for-sale, Total	$ 5,223,000	$ 4,638,000