Consolidated Statements of Shareholders' Equity (USD $) In Thousands	Common Stock [Member]	Retained Earnings [Member]	Total
Balance at April 30 at Apr. 30, 2011	$ 3,996	$ 399,900	$ 403,896
Net income		114,694	114,694
Dividends declared		(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 April 30 at Apr. 30, 2012	12,199	491,745	503,944
Net income		103,814	103,814
Dividends declared		(25,291)	(25,291)
Proceeds from exercise of stock options	4,721		4,721
Tax benefits related to nonqualified stock options	1,929		1,929
Stock based compensation	4,270		4,270
Balance at April 30 at Apr. 30, 2013	23,119	570,268	593,387
Net income		126,820	126,820
Dividends declared		(27,702)	(27,702)
Proceeds from exercise of stock options	3,368		3,368
Tax benefits related to nonqualified stock options	1,791		1,791
Stock based compensation	5,600		5,600
Balance at April 30 at Apr. 30, 2014	$ 33,878	$ 669,386	$ 703,264