Note 4 - Investments - Components of EAM's Investment Management Operations (Details) - USD ($) $ in Thousands		12 Months Ended
		Apr. 30, 2021	Dec. 31, 2020	Apr. 30, 2020	Dec. 31, 2019	Apr. 30, 2019
Revenues		$ 40,392		$ 40,299		$ 36,257
Non-voting revenues interest in EAM		15,190		11,184		8,260
EAM's net income (1)		23,280	$ 14,943	14,943	$ 12,009	12,009
EAM Trust [Member]
Other income		361		(156)		273
Investment management fee waivers and reimbursements		121		302		421
12b-1 fee waivers		651		667		654
Non-voting revenues interest in EAM		15,190		11,184		8,260
EAM's net income (1)	[1]	4,262		2,332		2,098
EAM Trust [Member] | Investment Advice [Member]
Revenues		29,022		21,985		16,715
EAM Trust [Member] | Distribution and Shareholder Service [Member]
Revenues		$ 9,604		$ 8,436		$ 6,811

[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.