Note K - Stock-based Compensation Plans - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Apr. 30, 2023	Apr. 30, 2022	Apr. 30, 2021	Apr. 30, 2020
Statement [Line Items]
Number of Shares (in shares)	501,400	566,400	667,750
Proceeds on Exercise	$ 47,480,000	$ 39,232,000	$ 41,026,000	$ 45,777,000
Weighted Average Exercise Price (in dollars per share)	$ 78.25	$ 72.43	$ 68.55
Number of Shares, Granted (in shares)	140,000	30,000	30,000
Exercise Price, Granted (in dollars per share)	$ 69.19	$ 150.83	$ 65.95
Proceeds on Exercise, Granted	$ 9,687,000	$ 4,525,000	$ 1,979,000
Number of Shares, Exercised (in shares)	(28,000)	(94,000)	(131,350)
Exercise Price, Exercised (in dollars per share)	$ 51.38	$ 66.76	$ 51.24
Proceeds on Exercise, Exercised	$ (1,439,000)	$ (6,276,000)	$ (6,730,000)
Number of Shares, Cancelled (in shares)	0	(1,000)	0
Proceeds on Exercise, Cancelled	$ 0	$ (42,000)	$ 0
Exercise Price, Cancelled (in dollars per share)		$ 41.86
Number of Shares (in shares)	613,400	501,400	566,400	667,750
Weighted Average Exercise Price (in dollars per share)	$ 77.41	$ 78.25	$ 72.43	$ 68.55
Minimum [Member]
Statement [Line Items]
Exercise Price, Exercised (in dollars per share)	44.52	24.37	24.69
Maximum [Member]
Statement [Line Items]
Exercise Price, Exercised (in dollars per share)	$ 53.02	$ 150.83	$ 99.05