Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Oct. 31, 2020	Apr. 30, 2020
Supplemental type certificates, accumulated amortization	$ 7,522	$ 7,029
Other assets, accumulated amortization	$ 10,524	$ 10,153
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, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	77,719,677	77,719,677
Common stock, shares outstanding (in shares)	74,033,347	74,398,262
Treasury stock, shares (in shares)	3,686,330	3,321,415
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	$ 100
Preferred stock, redemption value	$ 100	$ 100
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	$ 1,000
Preferred stock, redemption value	$ 1,000	$ 1,000
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