Note K - Stock-based Compensation Plans - Stock Incentive Plan (Details) - Stock Incentive Plan [Member]	12 Months Ended
	Apr. 30, 2017 $ / shares shares
Unvested shares (in shares)	9,500
Unvested shares, weighted average grant date fair value (in dollars per share) | $ / shares	$ 52.10
Shares granted (in shares)	10,000
Shares granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 39.14
Shares vested (in shares)	0
Shares cancelled (in shares)	(2,500)
Shares cancelled, weighted average grant date fair value (in dollars per share) | $ / shares	$ 49.51
Unvested shares (in shares)	17,000
Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 44.86