Note 2 - Investments (Details Textual) - USD ($)		3 Months Ended		6 Months Ended		12 Months Ended
		Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019	Apr. 30, 2020	Apr. 30, 2019
Available-for-sale Equity Securities, Amortized Cost Basis, Total		$ 15,909,000		$ 15,909,000		$ 12,877,000
Available-for-sale Securities, Equity Securities		17,185,000		17,185,000		$ 14,125,000
Proceeds from Sale of Available-for-sale Securities, Equity				5,529,000
Net Income (Loss) Attributable to Parent, Total		$ 5,056,000	$ 4,211,000	10,173,000	7,901,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent, Total				(35,000)	457,000
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax				$ 232,000	95,000
Available-for-sale Securities, Debt Securities, Average Yield		2.47%		2.47%		2.27%
Equity Method Investments		$ 60,351,000		$ 60,351,000		$ 59,165,000
EAM Trust [Member]
Net Income (Loss) Attributable to Parent, Total	[1]	970,000	$ 580,000	1,698,000	1,146,000
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
Percentage of Non Voting Profit Interest						50.00%
Accrued Non Voting Revenues and Non Voting Profits Interests Payable		4,165,000		4,165,000		$ 2,949,000
Equity Securities [Member]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent, Total				27,000	403,000
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax				7,000	84,000
Available-for-sale Securities, Gross Realized Gain (Loss), Total					0
AOCI, Debt Securities, Available-for-sale, Adjustment, after Tax, Total		1,276,000		1,276,000		1,248,000
AOCI Tax, Attributable to Parent		332,000		332,000		324,000
Debt Securities [Member]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent, Total				(62,000)	54,000
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax				(16,000)	11,000
AOCI, Debt Securities, Available-for-sale, Adjustment, after Tax, Total		115,000		115,000		177,000
AOCI Tax, Attributable to Parent		$ 30,000		30,000		$ 46,000
Proceeds from Sale and Maturity of Debt Securities, Available-for-sale, Total				5,214,000	$ 4,974,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity Securities [Member] | AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Net Income (Loss) Attributable to Parent, Total				$ 925,000

[1] Represents EAM's net income, after giving effect to Value Line's non-voting revenues interest, but before distributions to voting profits interest holders and to the Company in respect of its 50% non-voting profits interest.