Note K - Stock-based Compensation Plans - Stock Incentive Plan (Details) - Stock Incentive Plan [Member] - $ / shares	12 Months Ended
	Apr. 30, 2022	Apr. 30, 2021	Apr. 30, 2020
Unvested shares (in shares)	192,018	184,828	180,500
Unvested shares, weighted average grant date fair value (in dollars per share)	$ 51.70	$ 49.71	$ 46.16
Shares granted (in shares)	11,287	7,690	12,328
Shares granted, weighted average grant date fair value (in dollars per share)	$ 121.17	$ 98.43	$ 102.03
Shares vested (in shares)	(6,500)	0	(7,000)
Shares cancelled (in shares)	(15,691)	(500)	(1,000)
Shares cancelled, weighted average grant date fair value (in dollars per share)	$ 59.99	$ 35.00	$ 37.07
Shares vested, weighted average grant date fair value (in dollars per share)	$ 39.14	$ 0
Unvested shares (in shares)	181,114	192,018	184,828
Unvested shares, weighted average grant date fair value (in dollars per share)	$ 55.76	$ 51.70	$ 49.71