Earnings Per Share - Computation of EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Aug. 31, 2020	Aug. 31, 2019
Basic Earnings per Share
Net income	$ 300,005	$ 250,812
Less: income allocated to participating securities	2,173	2,016
Income available to common shareholders	$ 297,832	$ 248,796
Basic weighted average common shares outstanding (in shares)	104,110	103,543
Basic earnings per share (in dollars per share)	$ 2.86	$ 2.40
Diluted Earnings per Share
Net income	$ 300,005	$ 250,812
Less: income allocated to participating securities	2,173	2,016
Income available to common shareholders	$ 297,832	$ 248,796
Basic weighted average common shares outstanding (in shares)	104,110	103,543
Effect of dilutive securities - employee stock options (in shares)	3,019	3,540
Diluted weighted average common shares outstanding (in shares)	107,129	107,083
Diluted earnings per share (in dollars per share)	$ 2.78	$ 2.32