Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
Basic Earnings per Share from Continuing Operations
Income from continuing operations	$ 161,108	$ 136,208
Less: income from continuing operations allocated to participating securities	3,187	2,852
Income from continuing operations available to common shareholders	$ 157,921	$ 133,356
Basic weighted average common shares outstanding (in shares)	105,740	104,483
Basic earnings per share from continuing operations (in dollars per share)	$ 1.50	$ 1.27
Diluted Earnings per Share from Continuing Operations
Income from continuing operations	$ 161,108	$ 136,208
Less: income from continuing operations allocated to participating securities	3,187	2,852
Income from continuing operations available to common shareholders	$ 157,921	$ 133,356
Basic weighted average common shares outstanding (in shares)	105,740	104,483
Effect of dilutive securities - employee stock options (in shares)	2,797	2,631
Diluted weighted average common shares outstanding (in shares)	108,537	107,114
Diluted earnings per share from continuing operations (in dollars per share)	$ 1.45	$ 1.24