Note 7 - Related Party Transactions (Details Textual) - USD ($)	3 Months Ended						9 Months Ended		21 Months Ended
	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Apr. 30, 2017
Percentage of Non Voting Profits Interests Due from Ex Subsidiary Payable to Parent under Agreement							90.00%
Percent of Revenue Interest							100.00%
Federal Income Tax Payments to Parent							$ 3,450,000	$ 5,250,000
Ownership Percentage By Parent	89.00%						89.00%		89.00%
Value Line Inc [Member]
Accounts Receivable, Related Parties	$ 0						$ 0		$ 0	$ 0
Value Line Inc [Member]
Reimbursement Revenue							242,000		252,000
EAM Trust [Member]
Assets under Management, Carrying Amount	$ 2,600,000,000			$ 2,300,000,000			$ 2,600,000,000	$ 2,300,000,000	2,600,000,000
Percentage of Assets Increased (Decreased) in Unconsolidated Entities							13.00%
Non Voting Profits Interest Percent							50.00%
Percentage of Non Voting Profits Interests Due from Ex Subsidiary Payable to Parent under Agreement							90.00%
Percentage of Non Voting Revenues Interest in Unconsolidated Entity	50.88%	50.28%	49.73%	49.19%	49.14%	49.45%
Accrued Non Voting Revenues and Non Voting Profits Interests Payable	$ 2,261,000						$ 2,261,000		$ 2,261,000	$ 1,919,000
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%