Consolidated Statements Of Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Beginning Balances, Value at Apr. 30, 2011	$ 1,449,574	$ 4,124	$ 812,666	$ 11,233	$ 2,658,103	$ (2,036,552)
Beginning Balances, Shares		(397,887)				(105,768)
Net income	265,932				265,932
Other comprehensive income (loss)	912			912
Unrealized translation gain	(2,186)
Change in net unrealized gain on available-for-sale securities	3,098
Stock-based compensation	14,968		14,968
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures	6,383		(22,118)		(125)	28,626
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures						1,505
Shares issued for:
Acquisition of treasury shares, shares						(198)
Acquisition of treasury shares, value	(3,087)					(3,087)
Repurchase and retirement of common shares, shares	(14,554)	(14,554)
Repurchase and retirement of common shares, value	(199,989)	(145)	(8,732)		(191,112)
Cash dividends declared and paid	(208,801)				(208,801)
Ending Balances, Value at Apr. 30, 2012	1,325,892	3,979	796,784	12,145	2,523,997	(2,011,013)
Ending Balances, Shares at Apr. 30, 2012		(397,887)				(105,768)
Beginning Balances, Shares		(316,628)				(43,993)
Net income	433,948				433,948
Other comprehensive income (loss)	(1,595)			(1,595)
Unrealized translation gain	(1,760)
Change in net unrealized gain on available-for-sale securities	165
Stock-based compensation	15,293		15,293
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures	25,138		(11,652)		(257)	37,047
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures						1,949
Shares issued for:
Acquisition of treasury shares, shares						(174)
Acquisition of treasury shares, value	(2,928)					(2,928)
Repurchase and retirement of common shares, shares	(21,259)	(21,259)
Repurchase and retirement of common shares, value	(315,000)	(213)	(12,542)		(302,245)
Treasury Stock, Shares, Retired		60,000				60,000
Treasury Stock, Retired, Cost Method, Amount	0	600	35,400		1,104,797	1,140,797
Cash dividends declared	(217,201)				(217,201)
Ending Balances, Value at Apr. 30, 2013	1,263,547	3,166	752,483	10,550	1,333,445	(836,097)
Ending Balances, Shares at Apr. 30, 2013		(316,628)				(43,993)
Beginning Balances, Shares		(316,628)				(42,400)
Net income	475,157				475,157
Other comprehensive income (loss)	(5,373)			(5,373)
Unrealized translation gain	(3,475)
Change in net unrealized gain on available-for-sale securities	(1,898)
Stock-based compensation	20,058		20,058
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures	28,246		(5,887)		(325)	34,458
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures						1,811
Shares issued for:
Option exercises, shares	1,179
Acquisition of treasury shares, shares						(218)
Acquisition of treasury shares, value	(6,106)					(6,106)
Repurchase and retirement of common shares, shares	0
Repurchase and retirement of common shares, value	0
Treasury Stock, Shares, Retired	60,000
Cash dividends declared	(218,980)				(218,980)
Ending Balances, Value at Apr. 30, 2014	1,556,549	3,166	766,654	5,177	1,589,297	(807,745)
Ending Balances, Shares at Apr. 30, 2014		(316,628)				(42,400)
Beginning Balances, Value at Jan. 31, 2014
Beginning Balances, Shares		(316,628)
Net income	909,998
Ending Balances, Value at Apr. 30, 2014	$ 1,556,549	$ 3,166
Ending Balances, Shares at Apr. 30, 2014		(316,628)