Consolidated Statements Of Shareholders' Equity (USD $) In Thousands	Common Stock [Member]	Retained Earnings [Member]	Total
Balance at Apr. 30, 2009	$ 60,804	$ 660,226	$ 721,030
Net earnings		116,962	116,962
Payments of cash dividends		(17,308)	(17,308)
Proceeds from exercise of stock options	1,239		1,239
Tax benefits related to nonqualified stock options	365		365
Stock based compensation	2,031		2,031
Balance at Apr. 30, 2010	64,439	759,880	824,319
Net earnings		94,623	94,623
Payments of cash dividends		(20,467)	(20,467)
Repurchase of common stock	(66,890)	(434,136)	(501,026)
Proceeds from exercise of stock options	3,733		3,733
Tax benefits related to nonqualified stock options	648		648
Stock based compensation	2,066		2,066
Balance at Apr. 30, 2011	3,996	399,900	403,896
Net earnings		116,791	116,791
Payments of cash dividends		(22,849)	(22,849)
Proceeds from exercise of stock options	3,249		3,249
Tax benefits related to nonqualified stock options	1,162		1,162
Stock based compensation	3,792		3,792
Balance at Apr. 30, 2012	$ 12,199	$ 493,842	$ 506,041