Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 29, 2016	Feb. 28, 2015	Feb. 29, 2016	Feb. 28, 2015
Basic Earnings per Share from Continuing Operations
Income from continuing operations	$ 117,279	$ 100,331	$ 338,930	$ 309,937
Less: income from continuing operations allocated to participating securities	1,871	733	5,500	2,666
Income from continuing operations available to common shareholders	$ 115,408	$ 99,598	$ 333,430	$ 307,271
Basic weighted average common shares outstanding (shares)	107,843	116,178	108,923	116,653
Basic earnings per common share:
Basic earnings per share, continuing operations (dollars per share)	$ 1.07	$ 0.86	$ 3.06	$ 2.64
Diluted Earnings per Share from Continuing Operations
Income from continuing operations	$ 117,279	$ 100,331	$ 338,930	$ 309,937
Less: income from continuing operations allocated to participating securities	1,871	733	5,500	2,666
Income from continuing operations available to common shareholders	$ 115,408	$ 99,598	$ 333,430	$ 307,271
Basic weighted average common shares outstanding (shares)	107,843	116,178	108,923	116,653
Effect of dilutive securities - employee stock options (shares)	1,620	1,689	1,689	1,561
Diluted weighted average common shares outstanding (shares)	109,463	117,867	110,612	118,214
Diluted earnings per share:
Diluted earnings per share from continuing operations (dollars per share)	$ 1.05	$ 0.85	$ 3.01	$ 2.60