Note 2 - Investments (Details Textual) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Oct. 31, 2021	Oct. 31, 2020	Oct. 31, 2021	Oct. 31, 2020	Apr. 30, 2021
Equity Securities, FV-NI, Cost	$ 21,887,000		$ 21,887,000		$ 19,105,000
Equity Securities, FV-NI, Total	26,685,000		26,685,000		23,582,000
Proceeds from Sale of Equity Securities, FV-NI			687,000	$ 5,529,000
Proceeds from Sale and Maturity of Debt Securities, Available-for-sale, Total			2,496,000	5,214,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent, Total	0	$ (9,000)	(4,000)	(46,000)
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax			(1,000)	$ (16,000)
Equity Securities, FV-NI, Gain (Loss), Total			35,000		925,000
Equity Method Investments	61,058,000		61,058,000		60,977,000
EAM Trust [Member]
Fair Value of Contributed Capital at Inception	55,805,000		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		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	4,830,000		$ 4,830,000		4,664,000
Fixed Income Securities [Member]
AOCI, Debt Securities, Available-for-sale, Adjustment, after Tax, Total	$ 727		727		4,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent, Total			(5,000)		(173,000)
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax			$ (1,000)		$ (45,000)
Debt Securities, Available-for-Sale, Weighted Average Yield	0.22%		0.22%		1.40%
Fixed Income Securities [Member] | AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
AOCI Tax, Attributable to Parent	$ 153		$ 153		$ 1,000