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, 2015	Nov. 30, 2014	Nov. 30, 2015	Nov. 30, 2014
Basic Earnings per Share from Continuing Operations
Income from continuing operations	$ 115,453	$ 103,701	$ 221,651	$ 209,606
Less: income from continuing operations allocated to participating securities	1,887	1,342	3,629	1,933
Income from continuing operations available to common shareholders	$ 113,566	$ 102,359	$ 218,022	$ 207,673
Basic weighted average common shares outstanding (shares)	108,301	117,115	109,455	116,887
Basic earnings per common share:
Basic earnings per share, continuing operations (dollars per share)	$ 1.05	$ 0.88	$ 1.99	$ 1.78
Diluted Earnings per Share from Continuing Operations
Income from continuing operations	$ 115,453	$ 103,701	$ 221,651	$ 209,606
Less: income from continuing operations allocated to participating securities	1,887	1,342	3,629	1,933
Income from continuing operations available to common shareholders	$ 113,566	$ 102,359	$ 218,022	$ 207,673
Basic weighted average common shares outstanding (shares)	108,301	117,115	109,455	116,887
Effect of dilutive securities - employee stock options (shares)	1,812	1,540	1,685	1,447
Diluted weighted average common shares outstanding (shares)	110,113	118,655	111,140	118,334
Diluted earnings per share:
Diluted earnings per share from continuing operations (dollars per share)	$ 1.03	$ 0.86	$ 1.96	$ 1.75