Consolidated Statements of Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Paid-In Capital	Retained Earnings	Other Accumulated Comprehensive Income (Loss)	Treasury Stock
Balance at May. 31, 2009	$ 2,367,409	$ 129,215	$ 72,364	$ 2,938,419	$ 25,299	$ (797,888)
Balance (in shares) at May. 31, 2009		173,086				(20,296)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	215,620			215,620
Equity adjustment for foreign currency translation	9,365				9,365
Change in fair value of derivatives, net of ($260), $3,813, and $3,091 of tax expense (benefit)	443				443
Amortization of interest rate lock agreements	767				767
Change in fair value of available-for-sale securities, net of $14, $0, and ($13) of tax expense (benefit)	(28)				(28)
Comprehensive income, net of tax	226,167
Dividends	(73,960)			(73,960)
Stock-based compensation	15,349		15,349
Vesting of stock-based compensation awards (in shares)		121
Vesting of stock-based compensation awards		2,843	(2,843)
Stock options exercised, net of shares surrendered (in shares)	0
Repurchase of common stock (in shares)						(42)
Repurchase of common stock	(969)					(969)
Other	33		(254)		287
Balance at May. 31, 2010	2,534,029	132,058	84,616	3,080,079	36,133	(798,857)
Balance (in shares) at May. 31, 2010		173,207				(20,338)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	246,989			246,989
Equity adjustment for foreign currency translation	27,344				27,344
Change in fair value of derivatives, net of ($260), $3,813, and $3,091 of tax expense (benefit)	(6,096)				(6,096)
Amortization of interest rate lock agreements	767				767
Change in fair value of available-for-sale securities, net of $14, $0, and ($13) of tax expense (benefit)	3				3
Comprehensive income, net of tax	269,007
Dividends	(71,812)			(71,812)
Stock-based compensation	15,203		15,203
Vesting of stock-based compensation awards (in shares)		139
Vesting of stock-based compensation awards		3,343	(3,343)
Stock options exercised, net of shares surrendered (in shares)	0
Repurchase of common stock (in shares)						(15,424)
Repurchase of common stock	(443,690)					(443,690)
Other	(88)		(744)		656
Balance at May. 31, 2011	2,302,649	135,401	95,732	3,255,256	58,807	(1,242,547)
Balance (in shares) at May. 31, 2011		173,346				(35,762)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	297,637			297,637
Equity adjustment for foreign currency translation	(17,815)				(17,815)
Change in fair value of derivatives, net of ($260), $3,813, and $3,091 of tax expense (benefit)	(5,286)				(5,286)
Amortization of interest rate lock agreements	1,508				1,508
Change in fair value of available-for-sale securities, net of $14, $0, and ($13) of tax expense (benefit)	24				24
Comprehensive income, net of tax	276,068
Dividends	(70,820)			(70,820)
Stock-based compensation	20,312		20,312
Vesting of stock-based compensation awards (in shares)		297
Vesting of stock-based compensation awards		9,513	(9,513)
Stock options exercised, net of shares surrendered (in shares)		103
Stock options exercised, net of shares surrendered	3,341	3,341
Repurchase of common stock (in shares)						(11,464)
Repurchase of common stock	(392,328)					(392,328)
Other	(87)		488		(575)
Balance at May. 31, 2012	$ 2,139,135	$ 148,255	$ 107,019	$ 3,482,073	$ 36,663	$ (1,634,875)
Balance (in shares) at May. 31, 2012		173,746				(47,226)