Consolidated Statements Of Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Convertible Preferred Stock	Additional Paid-in Capital	Accumulated	Retained Earnings	Treasury Stock
Beginning Balances, Value at Apr. 30, 2010	$ 1,440,630	$ 4,314		$ 832,604	$ 1,678	$ 2,658,586	$ (2,056,552)
Beginning Balances, Shares		412,441					107,075
Net income	406,110					406,110
Unrealized translation gain	9,427				9,427
Change in net unrealized gain on available-for-sale securities	128				128
Stock-based compensation	14,500			14,500
Shares issued for:
Option exercises, shares							339
Option exercises, value	(1,893)			(8,332)			6,439
Nonvested shares/units, shares							632
Nonvested shares/units, value	(1,019)			(12,952)		(95)	12,028
ESPP, shares							269
ESPP, value	3,337			(1,784)			5,121
Acquisition of treasury shares, shares							(230)
Acquisition of treasury shares, value	(3,588)						(3,588)
Repurchase and retirement of common shares, shares	(18,950)	(18,950)
Repurchase and retirement of common shares, value	(279,947)	(190)		(11,370)		(268,387)
Cash dividends declared	(138,111)					(138,111)
Ending Balances, Value at Apr. 30, 2011	1,449,574	4,124		812,666	11,233	2,658,103	(2,036,552)
Ending Balances, Shares at Apr. 30, 2011		(412,441)					(107,075)
Beginning Balances, Shares		397,887					105,768
Net income	265,932					265,932
Unrealized translation gain	(2,186)				(2,186)
Change in net unrealized gain on available-for-sale securities	3,098				3,098
Stock-based compensation	14,968			14,968
Shares issued for:
Option exercises, shares							658
Option exercises, value	4,634			(7,875)			12,509
Nonvested shares/units, shares							684
Nonvested shares/units, value	(227)			(13,113)		(125)	13,011
ESPP, shares							163
ESPP, value	1,976			(1,130)			3,106
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
Unrealized translation gain	(1,760)				(1,760)
Change in net unrealized gain on available-for-sale securities	165				165
Stock-based compensation	15,293			15,293
Shares issued for:
Option exercises, shares	1,414						1,414
Option exercises, value	24,115			(2,766)			26,881
Nonvested shares/units, shares							463
Nonvested shares/units, value	(15)			(8,551)		(257)	8,793
ESPP, shares							72
ESPP, value	1,038			(335)			1,373
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					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)