Supplemental Cash Flow Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010
Cash Flow Supplemental Disclosures [Line Items]
Interest paid, net of amount capitalized	$ 18,281	$ 17,358	$ 9,814
Income taxes paid, net of (refunds)	$ 46,445	$ 53,194	$ (1,601)