Consolidated Condensed Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Paid-In Capital	Retained Earnings	Other Accumulated Comprehensive Income (Loss)	Treasury Stock
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	0	$ 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
Comprehensive income (loss), net of tax	(15,931)
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	0	$ 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	0	$ 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)
Balance (shares) at May. 31, 2019		184,791				81,506
Balance at May. 31, 2019	3,002,721	$ 840,328	227,928	6,691,236	(39,152)	$ (4,717,619)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	250,812			250,812
Comprehensive income (loss), net of tax	(23,474)				(23,474)
Stock-based compensation	40,395		40,395
Vesting of stock-based compensation awards (shares)		605
Vesting of stock-based compensation awards	0	$ 157,882	(157,882)
Stock options exercised, net of shares surrendered (in shares)		557
Stock options exercised, net of shares surrendered	37,915	$ 37,915
Repurchase of common stock (shares)						(1,082)
Repurchase of common stock	(256,830)					$ (256,830)
Balance (shares) at Aug. 31, 2019		185,953				82,588
Balance at Aug. 31, 2019	3,050,706	$ 1,036,125	110,441	6,939,240	(60,651)	$ (4,974,449)
Balance (shares) at May. 31, 2019		184,791				81,506
Balance at May. 31, 2019	3,002,721	$ 840,328	227,928	6,691,236	(39,152)	$ (4,717,619)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	731,452
Comprehensive income (loss), net of tax	(57,637)
Balance (shares) at Feb. 29, 2020		186,632				82,605
Balance at Feb. 29, 2020	3,324,309	$ 1,092,074	154,157	7,151,838	(94,814)	$ (4,978,946)
Balance (shares) at Aug. 31, 2019		185,953				82,588
Balance at Aug. 31, 2019	3,050,706	$ 1,036,125	110,441	6,939,240	(60,651)	$ (4,974,449)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	246,120			246,120
Comprehensive income (loss), net of tax	23,816				23,816
Dividends	(268,050)			(268,050)
Stock-based compensation	29,003		29,003
Vesting of stock-based compensation awards (shares)		21
Vesting of stock-based compensation awards	0	$ 5,403	(5,403)
Stock options exercised, net of shares surrendered (in shares)		324
Stock options exercised, net of shares surrendered	25,286	$ 25,286
Repurchase of common stock (shares)						(7)
Repurchase of common stock	(1,911)					$ (1,911)
Balance (shares) at Nov. 30, 2019		186,298				82,595
Balance at Nov. 30, 2019	3,104,970	$ 1,066,814	134,041	6,917,310	(36,835)	$ (4,976,360)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	234,520			234,520
Comprehensive income (loss), net of tax	(57,979)				(57,979)
Dividends	8			8
Stock-based compensation	27,030		27,030
Vesting of stock-based compensation awards (shares)		25
Vesting of stock-based compensation awards	0	$ 6,914	(6,914)
Stock options exercised, net of shares surrendered (in shares)		309
Stock options exercised, net of shares surrendered	18,346	$ 18,346
Repurchase of common stock (shares)						(10)
Repurchase of common stock	(2,586)					$ (2,586)
Balance (shares) at Feb. 29, 2020		186,632				82,605
Balance at Feb. 29, 2020	$ 3,324,309	$ 1,092,074	$ 154,157	$ 7,151,838	$ (94,814)	$ (4,978,946)