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, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	[1]	Feb. 29, 2016	[1]	Nov. 30, 2015	[1]	Aug. 31, 2015	[1]	May 31, 2017	May 31, 2016	May 31, 2015
Diluted Earnings per Share from Continuing Operations
Income from continuing operations	$ 82,174	$ 116,954	$ 121,950	$ 136,208	$ 115,711		$ 115,122		$ 113,447		$ 104,325		$ 457,286	$ 448,605	$ 402,553
Less: income from continuing operations allocated to participating securities													8,168	7,131	3,771
Income from continuing operations available to common shareholders													$ 449,118	$ 441,474	$ 398,782
Basic weighted average common shares outstanding (shares)	105,325	105,093	104,957	104,483	106,136		107,843		108,301		110,597		104,964	108,221	115,900
Effect of dilutive securities - employee stock options (shares)													2,819	1,735	1,643
Diluted weighted average common shares outstanding (shares)													107,783	109,956	117,543
Diluted earnings per share:
Diluted earnings per share from continuing operations (in dollars per share)	$ 0.75	$ 1.06	$ 1.12	$ 1.24	$ 1.06		$ 1.03		$ 1.01		$ 0.92		$ 4.17	$ 4.02	$ 3.39

[1] The figures for fiscal 2016 reflect the change in classification of Discontinued Services as discontinued operations within the Consolidated Statements of Income. See Note 16 entitled Discontinued Operations for additional information.