Schedule of Combined Financial Information for Unconsolidated Affiliates (Detail) (USD $) In Thousands, unless otherwise specified	Feb. 28, 2013	May 31, 2012
Investments in and Advances to Affiliates [Line Items]
Current assets	$ 662,079	$ 626,975
Noncurrent assets	355,607	345,500
Total assets	1,017,686	972,475
Current liabilities	183,464	174,016
Current maturities of long-term debt	5,394	5,305
Long-term debt	273,870	289,308
Other noncurrent liabilities	23,461	21,934
Equity	531,497	481,912
Total liabilities and equity	$ 1,017,686	$ 972,475