Quarterly Financial Data (Schedule of Share Price and Dividends Paid) (Details) (USD $)	3 Months Ended								12 Months Ended
	Apr. 30, 2011	Jan. 31, 2011	Oct. 31, 2010	Jul. 31, 2010	Apr. 30, 2010	Jan. 31, 2010	Oct. 31, 2009	Jul. 31, 2009	Apr. 30, 2011	Apr. 30, 2010
Dividends paid per share	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.6	$ 0.6
High [Member]
Stock price range	$ 18.00	$ 13.79	$ 15.97	$ 18.99	$ 21.84	$ 23.23	$ 20.00	$ 17.85	$ 18.99	$ 23.23
Low [Member]
Stock price range	$ 12.46	$ 11.15	$ 10.13	$ 13.44	$ 15.90	$ 18.10	$ 16.41	$ 13.73	$ 10.13	$ 13.73