Earnings per Share - Computation of Diluted Earnings Per Share For Continuing Operations (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
Diluted Earnings per Share from Continuing Operations
Income from continuing operations	$ 189,298	$ 295,789	$ 137,737	$ 161,108	$ 82,174	$ 116,954	$ 121,950	$ 136,208	$ 783,932	$ 457,286	$ 448,605
Less: income from continuing operations allocated to participating securities									11,794	8,168	7,131
Income from continuing operations available to common shareholders									$ 772,138	$ 449,118	$ 441,474
Basic weighted average common 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
Effect of dilutive securities - employee stock options (shares)									3,217	2,819	1,735
Diluted weighted average common shares outstanding (shares)									109,810	107,783	109,956
Diluted earnings per share:
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