Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	May 31, 2016	May 31, 2015
Statement of Financial Position [Abstract]
Allowance on accounts receivable	$ 19,604	$ 15,674
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)	179,598,516	178,117,334
Common stock, shares outstanding (in shares)	104,213,479	111,702,949
Treasury stock, shares (in shares)	75,385,037	66,414,385