Note K - Stock-based Compensation Plans - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Apr. 30, 2022	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Number of Shares (in shares)	566,400	667,750	565,500
Proceeds on Exercise	$ 32,789	$ 39,077	$ 45,777	$ 26,087
Weighted Average Exercise Price (in dollars per share)	$ 72.43	$ 68.55	$ 46.13
Number of Shares, Granted (in shares)	30,000	30,000	225,000
Exercise Price, Granted (in dollars per share)	$ 150.83	$ 65.95	$ 107.95
Proceeds on Exercise, Granted	$ 30	$ 30	$ 24,287
Number of Shares, Exercised (in shares)	(94,000)	(131,350)	(121,250)
Exercise Price, Exercised (in dollars per share)	$ 66.76	$ 51.24	$ 37.25
Proceeds on Exercise, Exercised	$ (6,276)	$ (6,730)	$ (4,517)
Number of Shares, Cancelled (in shares)	(1,000)		(1,500)
Exercise Price, Cancelled (in dollars per share)	$ 41.86		$ 53.02
Proceeds on Exercise, Cancelled	$ (42)		$ (80)
Number of Shares (in shares)	501,400	566,400	667,750	565,500
Weighted Average Exercise Price (in dollars per share)		$ 72.43	$ 68.55	$ 46.13
Minimum [Member]
Exercise Price, Granted (in dollars per share)			99.05
Exercise Price, Exercised (in dollars per share)	26.37	24.69	22.87
Maximum [Member]
Exercise Price, Granted (in dollars per share)			109.06
Exercise Price, Exercised (in dollars per share)	$ 150.83	$ 99.05	$ 53.02