Note 2 - Investments (Details Textual) - USD ($)	3 Months Ended		6 Months Ended		9 Months Ended		12 Months Ended	15 Months Ended
	Jan. 31, 2022	Jan. 31, 2021	Jan. 31, 2022	Jan. 31, 2021	Jan. 31, 2022	Jan. 31, 2021	Apr. 30, 2021	Jan. 31, 2022
Equity Securities, FV-NI, Cost	$ 22,746,000		$ 22,746,000		$ 22,746,000		$ 19,105,000	$ 22,746,000
Equity Securities, FV-NI, Total	27,316,000		27,316,000		27,316,000		23,582,000	27,316,000
Proceeds from Sale of Equity Securities, FV-NI			1,202,000	$ 7,684,000	1,202,000	$ 7,684,000
Proceeds from Sale and Maturity of Debt Securities, Available-for-sale, Total					2,496,000	11,431,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent, Total	0	$ (59,000)			(4,000)	(105,000)		0
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax					(1,000)	$ (37,000)
Equity Securities, FV-NI, Gain (Loss), Total					30,000		1,162,000
Equity Method Investments	60,882,000		60,882,000		60,882,000		60,977,000	60,882,000
EAM Trust [Member]
Fair Value of Contributed Capital at Inception	55,805,000		55,805,000		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		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	4,600,000		4,600,000		$ 4,600,000		4,664,000	4,600,000
Fixed Income Securities [Member]
AOCI, Debt Securities, Available-for-sale, Adjustment, after Tax, Total	$ (1,000)		$ (1,000)		(1,000)		4,000	$ (1,000)
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%		0.22%		1.40%	0.22%
Fixed Income Securities [Member] | AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
AOCI Tax, Attributable to Parent	$ 278		$ 278		$ 278		$ 1,000	$ 278