Preferred And Common Stock (Schedule Of Range Of Exercise Prices And Weighted Average Remaining Contractual Life Of Outstanding Options) (Details) (USD $)	12 Months Ended
	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2009
Preferred And Common Stock [Line Items]
Exercise price	$ 44.39
Weighted average exercise price	$ 32.59	$ 23.38	$ 22.78	$ 20.45
Weighted average remaining contractual life of options outstanding (years)	7 years 2 months 12 days
11.86 - 17.64 [Member]
Preferred And Common Stock [Line Items]
Exercise price, lower range	$ 11.86
Exercise price, upper range	$ 17.64
Number of Shares, Outstanding	45,500
Stock options outstanding	45,500
Weighted average exercise price	$ 14.68
Weighted average remaining contractual life of options outstanding (years)	1 year 6 months
20.68 - 26.92 [Member]
Preferred And Common Stock [Line Items]
Exercise price, lower range	$ 20.68
Exercise price, upper range	$ 26.92
Number of Shares, Outstanding	569,009
Stock options outstanding	569,009
Weighted average exercise price	$ 24.92
Weighted average remaining contractual life of options outstanding (years)	6 years 1 month 6 days
44.39 [Member]
Preferred And Common Stock [Line Items]
Number of Shares, Outstanding	439,000
Stock options outstanding	439,000
Weighted average exercise price	$ 44.39
Weighted average remaining contractual life of options outstanding (years)	9 years 2 months 12 days