Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2016	Nov. 30, 2015	Nov. 30, 2016	Nov. 30, 2015
Basic Earnings per Share from Continuing Operations
Income from continuing operations	$ 123,454	$ 115,453	$ 261,545	$ 221,651
Less: income from continuing operations allocated to participating securities	2,228	1,887	4,955	3,629
Income from continuing operations available to common shareholders	$ 121,226	$ 113,566	$ 256,590	$ 218,022
Basic weighted average common shares outstanding (shares)	104,957	108,301	104,719	109,455
Basic earnings per common share:
Basic earnings per share from continuing operations (dollars per share)	$ 1.16	$ 1.05	$ 2.45	$ 1.99
Diluted Earnings per Share from Continuing Operations
Income from continuing operations	$ 123,454	$ 115,453	$ 261,545	$ 221,651
Less: income from continuing operations allocated to participating securities	2,228	1,887	4,955	3,629
Income from continuing operations available to common shareholders	$ 121,226	$ 113,566	$ 256,590	$ 218,022
Basic weighted average common shares outstanding (shares)	104,957	108,301	104,719	109,455
Effect of dilutive securities - employee stock options (shares)	2,690	1,812	2,559	1,685
Diluted weighted average common shares outstanding (shares)	107,647	110,113	107,278	111,140
Diluted earnings per share:
Diluted earnings per share from continuing operations (dollars per share)	$ 1.13	$ 1.03	$ 2.39	$ 1.96