Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2018	May 31, 2017	May 31, 2016
Quarterly Financial Data [Abstract]
Revenue	$ 1,669,550	$ 1,589,138	$ 1,606,441	$ 1,611,503	$ 1,530,287	$ 1,255,367	$ 1,271,077	$ 1,266,650	$ 6,476,632	$ 5,323,381	$ 4,795,772
Gross margin	752,338	700,463	716,369	739,353	678,726	559,924	565,218	576,427	2,908,523	2,380,295	2,101,340
Net income, continuing operations	$ 189,298	$ 295,789	$ 137,737	$ 161,108	$ 82,174	$ 116,954	$ 121,950	$ 136,208	$ 783,932	$ 457,286	$ 448,605
Basic earnings per share, continuing operations (dollars per share)	$ 1.74	$ 2.73	$ 1.27	$ 1.50	$ 0.76	$ 1.09	$ 1.15	$ 1.27	$ 7.24	$ 4.27	$ 4.08
Diluted earnings per share, continuing operations (in dollars per share)	$ 1.68	$ 2.66	$ 1.24	$ 1.45	$ 0.75	$ 1.06	$ 1.12	$ 1.24	$ 7.03	$ 4.17	$ 4.02
Weighted average number of shares outstanding (shares)	106,593	106,558	106,340	105,740	105,325	105,093	104,957	104,483	106,593	104,964	108,221