Note 7 - Related Party Transactions (Details Textual) - USD ($)	3 Months Ended		6 Months Ended
	Oct. 31, 2020	Jul. 31, 2020	Oct. 31, 2020	Oct. 31, 2019	Apr. 30, 2020
Federal Income Tax Payments to Parent			$ 3,660,000	$ 1,950,000
Ownership Percentage By Parent	89.92%		89.92%
Value Line Inc [Member]
Revenue from Related Parties			$ 206,000	191,000
Accounts Receivable, Related Parties	$ 0		0		$ 0
EAM Trust [Member]
Assets under Management, Carrying Amount	$ 4,460,000,000		$ 4,460,000,000	$ 3,500,000,000
Percentage of Assets Increased (Decreased) in Unconsolidated Entities			27.60%
Non Voting Profits Interest Percent		50.00%	50.00%
Percentage of Non Voting Revenues Interest in Unconsolidated Entity	52.06%
Accrued Non Voting Revenues and Non Voting Profits Interests Payable	$ 4,165,000		$ 4,165,000		$ 2,949,000
EAM Trust [Member] | Minimum [Member]
Non Voting Revenues Interest Percent			41.00%
Percentage of Non Voting Profits Interests Due from Ex Subsidiary Payable to Parent under Agreement			90.00%
EAM Trust [Member] | Maximum [Member]
Non Voting Revenues Interest Percent			55.00%