Note 7 - Related Party Transactions (Details Textual) - USD ($)	6 Months Ended
	Oct. 31, 2023	Oct. 31, 2022	Jul. 31, 2022	Apr. 30, 2022
Ownership Percentage By Parent	91.59%
AB&Co [Member]
Accounts Receivable, after Allowance for Credit Loss			$ 0	$ 0
Income Taxes Paid	$ 2,900,000	$ 3,127,000
AB&Co [Member] | Reimbursement for Payments and Services [Member]
Related Party Transaction, Amounts of Transaction	170,000	170,000
EAM Trust [Member]
Assets under Management, Carrying Amount	$ 3,310,000,000	$ 2,890,000,000
Percentage of Assets Increased (Decreased) in Unconsolidated Entities	14.50%
Non Voting Profits Interest Percent	50.00%
Voting Profits Interest Percent	50.00%
Accrued Investment Income Receivable	$ 2,967,000
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%