Consolidated Statements of Stockholders' Equity (USD $) In Thousands	Common Stock [Member]	Convertible Preferred Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Beginning Balances, Value at Apr. 30, 2008	$ 4,359		$ 695,959	$ 2,486	$ 2,384,449	$ (2,099,435)	$ 987,818
Beginning Balances, Shares at Apr. 30, 2008	435,891					(109,880)
Net income					485,673		485,673
Unrealized translation gain (loss)				(10,125)			(10,125)
Change in net unrealized gain (loss) on available-for-sale securities				(4,000)			(4,000)
Proceeds from common stock Issuance, net of expenses	83		141,332				141,415
Proceeds from common stock Issuance, net of expenses, shares	8,286
Stock-based compensation			32,600				32,600
Shares issued for:
Option exercises, shares						4,481
Option exercises, value			(12,624)			85,624	73,000
Nonvested shares/units, shares						1,015
Nonvested shares/units, value			(20,392)			19,402	(990)
ESPP, shares						292
ESPP, value			(423)			5,577	5,154
Acquisitions, shares						8
Acquisitions, value			25			163	188
Acquisition of treasury shares, shares						(5,991)
Acquisition of treasury shares, value						(106,189)	(106,189)
Cash dividends declared and paid					(198,685)		(198,685)
Ending Balances, Value at Apr. 30, 2009	4,442		836,477	(11,639)	2,671,437	(2,094,858)	1,405,859
Ending Balances, Shares at Apr. 30, 2009	444,177					(110,075)
Net income					479,242		479,242
Unrealized translation gain (loss)				14,442			14,442
Change in net unrealized gain (loss) on available-for-sale securities				(1,125)			(1,125)
Stock-based compensation			29,369				29,369
Shares issued for:
Option exercises, shares						1,293
Option exercises, value			(10,840)			24,616	13,776
Nonvested shares/units, shares						677
Nonvested shares/units, value			(13,806)		(300)	12,879	(1,227)
ESPP, shares						266
ESPP, value			(924)			5,058	4,134
Acquisition of treasury shares, shares						(246)
Acquisition of treasury shares, value						(4,247)	(4,247)
Retirement of common shares, value	(128)		(7,672)		(242,203)		(250,003)
Retirement of common shares, shares	(12,786)						(12,800)
Cash dividends declared					(48,691)		(48,691)
Cash dividends declared and paid					(200,899)		(200,899)
Ending Balances, Value at Apr. 30, 2010	4,314		832,604	1,678	2,658,586	(2,056,552)	1,440,630
Ending Balances, Shares at Apr. 30, 2010	431,391					(108,085)
Net income					406,110		406,110
Unrealized translation gain (loss)				9,427			9,427
Change in net unrealized gain (loss) on available-for-sale securities				128			128
Stock-based compensation			14,500				14,500
Shares issued for:
Option exercises, shares						339	338
Option exercises, value			(8,332)			6,439	(1,893)
Nonvested shares/units, shares						632
Nonvested shares/units, value			(12,952)		(95)	12,028	(1,019)
ESPP, shares						269
ESPP, value			(1,784)			5,121	3,337
Acquisition of treasury shares, shares						(230)
Acquisition of treasury shares, value						(3,588)	(3,588)
Retirement of common shares, value	(190)		(11,370)		(268,387)		(279,947)
Retirement of common shares, shares	(18,950)						(19,000)
Cash dividends declared					(138,111)		(138,111)
Ending Balances, Value at Apr. 30, 2011	$ 4,124		$ 812,666	$ 11,233	$ 2,658,103	$ (2,036,552)	$ 1,449,574
Ending Balances, Shares at Apr. 30, 2011	412,441					(107,075)