Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	May 31, 2012	May 31, 2011
Statement of Financial Position [Abstract]
Allowance on accounts receivable	$ 17,017	$ 17,057
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)	173,745,913	173,346,180
Common stock, shares outstanding (in shares)	126,519,758	137,583,884
Treasury stock, shares (in shares)	47,226,155	35,762,296