Note 3 - Related Party Transactions (Details Textual) - USD ($)	12 Months Ended
	Apr. 30, 2024	Apr. 30, 2023	Apr. 30, 2022
Ownership Percentage By Parent	91.63%
AB&Co [Member]
Accounts Receivable, after Allowance for Credit Loss	$ 0	$ 0
Income Taxes Paid	5,448,000	4,425,000	$ 5,400,000
AB&Co [Member] | Reimbursement for Payments and Services [Member]
Related Party Transaction, Amounts of Transaction	364,000	369,000
EAM Trust [Member]
Assets under Management, Carrying Amount	4,170,000,000	3,090,000,000.00
Increase (Decrease) in Assets under Management	$ 1,080,000,000.00
Percentage of Assets Increased (Decreased) in Unconsolidated Entities	35.00%
Non Voting Profits Interest Percent	50.00%
Voting Profits Interest Percent	50.00%
Non Voting Profits Interest in Variable Entity Not yet Paid	$ 3,865,000	$ 2,601,000
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%