Disclosure Of Compensation Related Costs, Share Based Payments (Schedule Of Issuance Of Stock Option Plans) (Details) (USD $)	6 Months Ended
	Oct. 31, 2011
Disclosure Of Compensation Related Costs, Share Based Payments [Abstract]
Number of Shares, Outstanding April 30, 2011	775,609
Number of Shares, Granted	441,000
Number of Shares, Exercised	(80,950)
Number of Shares, Forfeited	(3,500)
Number of Shares, Outstanding at October 31, 2011	1,132,159
Weighted Average Exercise Price, Outstanding April 30, 2011	$ 23.38
Weighted Average Exercise Price, Granted	$ 44.39
Weighted Average Exercise Price, Exercised	$ 20.28
Weighted Average Exercise Price, Forfeited	$ 36.19
Weighted Average Exercise Price, Outstanding at October 31, 2011	$ 31.75