Note 5 - Disclosure of Compensation Related Costs, Share Based Payments - Stock Option Activity (Details) (USD $)	6 Months Ended
	Oct. 31, 2014
Outstanding at October 31, 2014 (in shares)	564,974
Employee Stock Option [Member]
Outstanding at April 30, 2014 (in shares)	712,024
Outstanding at April 30, 2014 (in dollars per share)	$ 36.73
Exercised (in shares)	147,050
Exercised (in dollars per share)	$ 40.54
Outstanding at October 31, 2014 (in shares)	564,974
Outstanding at October 31, 2014 (in dollars per share)	$ 35.73