Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2019	May 31, 2018	May 31, 2017
Quarterly Financial Data [Abstract]
Revenue	$ 1,793,730	$ 1,682,330	$ 1,718,268	$ 1,697,975	$ 1,669,550	$ 1,589,138	$ 1,606,441	$ 1,611,503	$ 6,892,303	$ 6,476,632	$ 5,323,381
Gross margin	823,565	755,153	775,158	774,712	752,338	700,463	716,369	739,353	3,128,588	2,908,523	2,380,295
Net income, continuing operations	$ 226,171	$ 200,923	$ 242,994	$ 212,547	$ 189,298	$ 295,789	$ 137,737	$ 161,108	$ 882,635	$ 783,932	$ 457,286
Basic earnings per share, continuing operations (dollars per share)	$ 2.13	$ 1.89	$ 2.25	$ 1.96	$ 1.74	$ 2.73	$ 1.27	$ 1.50	$ 8.23	$ 7.24	$ 4.27
Diluted earnings per share, continuing operations (in dollars per share)	$ 2.06	$ 1.83	$ 2.18	$ 1.89	$ 1.68	$ 2.66	$ 1.24	$ 1.45	$ 7.97	$ 7.03	$ 4.17
Weighted average number of shares outstanding (shares)	105,018	105,080	106,475	106,835	106,593	106,558	106,340	105,740	106,080	106,593	104,964