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, 2017	Nov. 30, 2016	Nov. 30, 2017	Nov. 30, 2016
Basic Earnings per Share from Continuing Operations
Income from continuing operations	$ 137,737	$ 121,950	$ 298,845	$ 258,158
Less: income from continuing operations allocated to participating securities	2,111	1,923	5,298	4,775
Income from continuing operations available to common shareholders	$ 135,626	$ 120,027	$ 293,547	$ 253,383
Basic weighted average common shares outstanding (in shares)	106,340	104,957	106,039	104,719
Basic earnings per share from continuing operations (in dollars per share)	$ 1.27	$ 1.15	$ 2.77	$ 2.42
Diluted Earnings per Share from Continuing Operations
Income from continuing operations	$ 137,737	$ 121,950	$ 298,845	$ 258,158
Less: income from continuing operations allocated to participating securities	2,111	1,923	5,298	4,775
Income from continuing operations available to common shareholders	$ 135,626	$ 120,027	$ 293,547	$ 253,383
Basic weighted average common shares outstanding (in shares)	106,340	104,957	106,039	104,719
Effect of dilutive securities - employee stock options (in shares)	3,478	2,690	2,899	2,559
Diluted weighted average common shares outstanding (in shares)	109,818	107,647	108,938	107,278
Diluted earnings per share from continuing operations (in dollars per share)	$ 1.24	$ 1.12	$ 2.69	$ 2.36