Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	May 31, 2017	May 31, 2016
Statement of Financial Position [Abstract]
Allowance on accounts receivable	$ 20,525	$ 19,103
Preferred stock, shares authorized (in shares)	100,000	100,000
Preferred stock, shares outstanding ( in shares)	0	0
Common stock, shares authorized (in shares)	425,000,000	425,000,000
Common stock, shares issued (in shares)	180,992,605	179,598,516
Common stock, shares outstanding (in shares)	104,213,479	105,400,629
Treasury stock, shares (in shares)	75,591,976	75,385,037