Note 2 - Investments (Details Textual) - USD ($)	6 Months Ended		12 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Apr. 30, 2019
Available-for-sale Equity Securities, Amortized Cost Basis, Total	$ 9,447,000		$ 8,541,000
Available-for-sale Securities, Equity Securities	11,932,000		$ 10,622,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent, Total	457,000	$ 229,000
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	$ 95,000	48,000
Available-for-sale Securities, Debt Securities, Average Yield	2.25%		2.09%
Equity Method Investments	$ 59,186,000		$ 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	$ 3,028,000		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	403,000	227,000
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	84,000	48,000
AOCI, Debt Securities, Available-for-sale, Adjustment, after Tax, Total	2,485,000		2,081,000
AOCI Tax, Attributable to Parent	522,000		437,000
Debt Securities [Member]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent, Total	54,000	1,700
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	11,000	350
AOCI, Debt Securities, Available-for-sale, Adjustment, after Tax, Total	97,000		43,000
AOCI Tax, Attributable to Parent	21,000		$ 9,000
Proceeds from Sale and Maturity of Debt Securities, Available-for-sale, Total	$ 4,974,000	$ 4,638,000