Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Paid-In Capital	Retained Earnings	Other Accumulated Comprehensive Income (Loss)	Treasury Stock
Balance (shares) at May. 31, 2012		173,746,000				47,226,000
Beginning Balance at May. 31, 2012	$ 2,139,135	$ 148,255	$ 107,019	$ 3,482,073	$ 36,663	$ (1,634,875)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	315,442			315,442
Comprehensive income (loss), net of tax	1,460				1,460
Dividends	(79,744)			(79,744)
Stock-based compensation	23,310		23,310
Vesting of stock-based compensation awards (shares)		610,000
Vesting of stock-based compensation awards	$ 0	$ 23,270	(23,270)
Stock options exercised, net of shares surrendered (shares)	561,176	430,000
Stock options exercised, net of shares surrendered	$ 14,807	$ 14,807
Repurchase of common stock (shares)						(5,279,000)
Repurchase of common stock	(215,681)					$ (215,681)
Other	2,763		2,763
Balance (shares) at May. 31, 2013		174,786,000				52,505,000
Ending Balance at May. 31, 2013	2,201,492	$ 186,332	109,822	3,717,771	38,123	$ (1,850,556)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	374,442			374,442
Comprehensive income (loss), net of tax	(9,695)				(9,695)
Dividends	(93,320)			(93,320)
Stock-based compensation	44,746		44,746
Vesting of stock-based compensation awards (shares)		465,000
Vesting of stock-based compensation awards	$ 0	$ 23,519	(23,519)
Stock options exercised, net of shares surrendered (shares)	1,272,179	1,127,000
Stock options exercised, net of shares surrendered	$ 41,902	$ 41,902
Repurchase of common stock (shares)						(6,836,000)
Repurchase of common stock	(370,599)					$ (370,599)
Other	3,890		3,890
Balance (shares) at May. 31, 2014		176,378,000				59,341,000
Ending Balance at May. 31, 2014	2,192,858	$ 251,753	134,939	3,998,893	28,428	$ (2,221,155)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	430,618			430,618
Comprehensive income (loss), net of tax	(36,899)				(36,899)
Dividends	(201,891)			(201,891)
Stock-based compensation	47,002		47,002
Vesting of stock-based compensation awards (shares)		575,000
Vesting of stock-based compensation awards	$ 0	$ 37,265	(37,265)
Stock options exercised, net of shares surrendered (shares)	1,293,689	1,164,000
Stock options exercised, net of shares surrendered	$ 40,230	$ 40,230
Repurchase of common stock (shares)						(7,073,000)
Repurchase of common stock	(551,970)					$ (551,970)
Other	12,507		12,507
Balance (shares) at May. 31, 2015		178,117,000				66,414,000
Ending Balance at May. 31, 2015	$ 1,932,455	$ 329,248	$ 157,183	$ 4,227,620	$ (8,471)	$ (2,773,125)