Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($)	3 Months Ended	12 Months Ended
	Jul. 31, 2023	Apr. 30, 2023
Supplemental type certificates, accumulated amortization	$ 10,886,000	$ 10,603,000
Other assets, accumulated amortization	$ 12,469	$ 12,290
Preferred stock, par value (in dollars per share)	$ 5	$ 5
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	100,000,000	100,000,000
Common stock, issued (in shares)	79,571,211	80,871,211
Common stock, outstanding (in shares)	68,727,900	76,891,689
Treasury stock, shares (in shares)	10,843,311	3,979,522
Preferred Class A [Member]
Preferred stock, stated value (in dollars per share)	$ 100	$ 100
Preferred stock, dividend rate	9.80%	9.80%
Preferred stock, liquidation value	$ 100,000	$ 100,000
Preferred stock, redemption value	$ 100,000	$ 100,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Preferred stock, designated classes (in shares)	200,000	200,000
Preferred Class B [Member]
Preferred stock, stated value (in dollars per share)	$ 1,000	$ 1,000
Preferred stock, dividend rate	6.00%	6.00%
Preferred stock, liquidation value	$ 1,000,000	$ 1,000,000
Preferred stock, redemption value	$ 1,000,000	$ 1,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Preferred stock, designated classes (in shares)	200,000	200,000