Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Aug. 31, 2014	Aug. 31, 2013
Basic Earnings per Share from Continuing Operations
Income from continuing operations	$ 109,791	$ 77,398
Less: income from continuing operations allocated to participating securities	613	461
Income from continuing operations available to common shareholders	$ 109,178	$ 76,937
Basic weighted average common shares outstanding (shares)	116,659	122,130
Basic earnings per common share:
Total common shares, basic (dollars per share)	$ 0.94	$ 0.63
Diluted Earnings per Share from Continuing Operations
Basic weighted average common shares outstanding (shares)	116,659	122,130
Effect of dilutive securities - employee stock options & awards (shares)	1,371	762
Diluted weighted average common shares outstanding (shares)	118,030	122,892
Diluted earnings per share:
Total common shares, diluted (dollars per share)	$ 0.93	$ 0.63