Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	May 31, 2013	May 31, 2012
Statement of Financial Position [Abstract]
Allowance on accounts receivable	$ 15,855	$ 17,017
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)	174,786,010	173,745,913
Common stock, shares outstanding (in shares)	122,281,507	126,519,758
Treasury stock, shares (in shares)	52,504,503	47,226,155