Note 2 - Investments - Components of EAM's Investment Management Operations (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2021	Jan. 31, 2020
Revenues		$ 10,130	$ 10,803	$ 30,668	$ 30,500
Value Line’s non-voting revenues interest		4,104	3,033	11,113	8,389
Net Income (Loss) Attributable to Parent, Total		6,029	4,952	16,202	12,853
EAM Trust [Member]
Other income		119	89	234	147
Investment management fee waivers and reimbursements		88	15	207	233
12b-1 fee waivers		168	178	490	517
Value Line’s non-voting revenues interest		4,104	3,033	11,113	8,389
Net Income (Loss) Attributable to Parent, Total	[1]	1,260	844	2,958	1,990
EAM Trust [Member] | Investment Advice [Member]
Revenues		7,827	5,921	21,318	16,531
EAM Trust [Member] | Distribution and Shareholder Service [Member]
Revenues		$ 2,439	$ 2,210	$ 7,194	$ 6,275

[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.