Fair Value and Carrying Value of Financial Instruments and Long-Term Debt (Detail) (USD $) In Thousands, unless otherwise specified	Aug. 31, 2013	May 31, 2013	Aug. 31, 2012	May 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, carrying value	$ 204,903	$ 343,554	$ 257,382	$ 315,968
Marketable equity securities, carrying value	91,548	90,292
Marketable debt securities, carrying value	22,302	22,801
Long-term debt, including current portion, carrying value	1,424,144	1,373,697
Cash and cash equivalents, fair value	204,903	343,554
Marketable securities, fair value	113,850	113,093
Long-term debt, including current portion, fair value	1,504,714	1,501,850
Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities, fair value	91,548	90,292
Fixed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities, fair value	$ 22,302	$ 22,801