Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	May 31, 2014	May 31, 2013
Statement of Financial Position [Abstract]
Allowance on accounts receivable	$ 14,906	$ 15,855
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)	176,378,412	174,786,010
Common stock, shares outstanding (in shares)	117,037,784	122,281,507
Treasury stock, shares (in shares)	59,340,628	52,504,503