Note 7 - Related Party Transactions (Details Textual) - USD ($)	9 Months Ended
	Jan. 31, 2024	Jan. 31, 2023	Apr. 30, 2023
Ownership Percentage By Parent	91.59%
AB&Co [Member]
Accounts Receivable, after Allowance for Credit Loss	$ 0		$ 0
Income Taxes Paid	4,000,000	$ 3,327,000
AB&Co [Member] | Reimbursement for Payments and Services [Member]
Related Party Transaction, Amounts of Transaction	230,000	232,000
EAM Trust [Member]
Assets under Management, Carrying Amount	$ 4,060,000,000.00	$ 3,040,000,000.00
Percentage of Assets Increased (Decreased) in Unconsolidated Entities	33.60%
Non Voting Profits Interest Percent	50.00%
Voting Profits Interest Percent	50.00%
Accrued Investment Income Receivable	$ 3,448,000
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%