Consolidated Condensed Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Paid-In Capital	Retained Earnings	Other Accumulated Comprehensive Income	Treasury Stock
Balance (shares) at May. 31, 2017		180,993				75,592
Balance at May. 31, 2017	$ 2,302,793	$ 485,068	$ 223,924	$ 5,170,830	$ (3,029)	$ (3,574,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	217,211			217,211
Comprehensive income (loss), net of tax	35,032				35,032
Dividends	(1)			(1)
Stock-based compensation	28,630		28,630
Vesting of stock-based compensation awards (shares)		656
Vesting of stock-based compensation awards		$ 84,040	(84,040)
Stock options exercised, net of shares surrendered (in shares)		395
Stock options exercised, net of shares surrendered	17,256	$ 17,256
Repurchase of common stock (shares)						(272)
Repurchase of common stock	(35,040)					$ (35,040)
Balance (shares) at Aug. 31, 2017		182,044				75,864
Balance at Aug. 31, 2017	2,565,881	$ 586,364	168,514	5,388,040	32,003	$ (3,609,040)
Balance (shares) at May. 31, 2017		180,993				75,592
Balance at May. 31, 2017	2,302,793	$ 485,068	223,924	5,170,830	(3,029)	$ (3,574,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	656,415
Balance (shares) at Feb. 28, 2018		182,558				75,877
Balance at Feb. 28, 2018	2,893,997	$ 611,485	219,389	5,651,656	22,517	$ (3,611,050)
Balance (shares) at Aug. 31, 2017		182,044				75,864
Balance at Aug. 31, 2017	2,565,881	$ 586,364	168,514	5,388,040	32,003	$ (3,609,040)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	137,109			137,109
Comprehensive income (loss), net of tax	(11,566)				(11,566)
Dividends	(175,610)			(175,610)
Stock-based compensation	26,574		26,574
Vesting of stock-based compensation awards (shares)		18
Vesting of stock-based compensation awards		$ 2,897	(2,897)
Stock options exercised, net of shares surrendered (in shares)		277
Stock options exercised, net of shares surrendered	11,302	$ 11,302
Repurchase of common stock (shares)						(5)
Repurchase of common stock	(657)					$ (657)
Balance (shares) at Nov. 30, 2017		182,339				75,869
Balance at Nov. 30, 2017	2,553,033	$ 600,563	192,191	5,349,539	20,437	$ (3,609,697)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	302,095			302,095
Comprehensive income (loss), net of tax	2,080				2,080
Dividends	22			22
Stock-based compensation	30,840		30,840
Vesting of stock-based compensation awards (shares)		22
Vesting of stock-based compensation awards		$ 3,642	(3,642)
Stock options exercised, net of shares surrendered (in shares)		197
Stock options exercised, net of shares surrendered	7,280	$ 7,280
Repurchase of common stock (shares)						(8)
Repurchase of common stock	(1,353)					$ (1,353)
Balance (shares) at Feb. 28, 2018		182,558				75,877
Balance at Feb. 28, 2018	2,893,997	$ 611,485	219,389	5,651,656	22,517	$ (3,611,050)
Balance (shares) at May. 31, 2018		182,723				76,397
Balance at May. 31, 2018	3,016,526	$ 618,464	245,211	5,837,827	16,343	$ (3,701,319)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	212,515			212,515
Comprehensive income (loss), net of tax	(6,482)				(6,482)
Dividends	1			1
Stock-based compensation	46,172		46,172
Vesting of stock-based compensation awards (shares)		739
Vesting of stock-based compensation awards		$ 151,012	(151,012)
Stock options exercised, net of shares surrendered (in shares)		594
Stock options exercised, net of shares surrendered	27,512	$ 27,512
Repurchase of common stock (shares)						(689)
Repurchase of common stock	(139,468)					$ (139,468)
Balance (shares) at Aug. 31, 2018		184,056				77,086
Balance at Aug. 31, 2018	3,345,968	$ 796,988	140,371	6,239,535	9,861	$ (3,840,787)
Balance (shares) at May. 31, 2018		182,723				76,397
Balance at May. 31, 2018	3,016,526	$ 618,464	245,211	5,837,827	16,343	$ (3,701,319)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	658,862
Balance (shares) at Feb. 28, 2019		184,559				79,627
Balance at Feb. 28, 2019	3,179,492	$ 826,175	197,327	6,465,121	412	$ (4,309,543)
Balance (shares) at Aug. 31, 2018		184,056				77,086
Balance at Aug. 31, 2018	3,345,968	$ 796,988	140,371	6,239,535	9,861	$ (3,840,787)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	243,013			243,013
Comprehensive income (loss), net of tax	(5,996)				(5,996)
Dividends	(220,792)			(220,792)
Stock-based compensation	28,612		28,612
Vesting of stock-based compensation awards (shares)		11
Vesting of stock-based compensation awards		$ 2,146	(2,146)
Stock options exercised, net of shares surrendered (in shares)		86
Stock options exercised, net of shares surrendered	5,100	$ 5,100
Repurchase of common stock (shares)						(1,943)
Repurchase of common stock	(368,661)					$ (368,661)
Balance (shares) at Nov. 30, 2018		184,153				79,029
Balance at Nov. 30, 2018	3,027,244	$ 804,234	166,837	6,261,756	3,865	$ (4,209,448)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	203,334			203,334
Comprehensive income (loss), net of tax	(3,453)				(3,453)
Dividends	31			31
Stock-based compensation	30,769		30,769
Vesting of stock-based compensation awards (shares)		2
Vesting of stock-based compensation awards		$ 279	(279)
Stock options exercised, net of shares surrendered (in shares)		404
Stock options exercised, net of shares surrendered	21,662	$ 21,662
Repurchase of common stock (shares)						(598)
Repurchase of common stock	(100,095)					$ (100,095)
Balance (shares) at Feb. 28, 2019		184,559				79,627
Balance at Feb. 28, 2019	$ 3,179,492	$ 826,175	$ 197,327	$ 6,465,121	$ 412	$ (4,309,543)