Summary of Long-term Debt and Short-term Borrowings Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	May 31, 2014	May 31, 2013
Debt Instrument [Line Items]
Debt	$ 666,325	$ 521,056
current maturities and short-term borrowings	111,535	114,820
Total long-term debt	554,790	406,236
Short-term borrowings
Debt Instrument [Line Items]
Debt	10,362	113,728
Floating rate senior notes due December 17, 2014
Debt Instrument [Line Items]
Debt	100,000	100,000
6.50% senior notes due April 15, 2020
Debt Instrument [Line Items]
Debt	149,912	149,888
4.60% senior notes due August 10, 2024
Debt Instrument [Line Items]
Debt	150,000	150,000
Unsecured Senior Notes, Four Point Five Five Percent, Due April Fifteen Twenty Twenty Six
Debt Instrument [Line Items]
Debt	249,472
Industrial revenue bonds due April 2019
Debt Instrument [Line Items]
Debt	2,024	2,084
Secured Term Loan
Debt Instrument [Line Items]
Debt	4,235	5,036
Other Debt
Debt Instrument [Line Items]
Debt	$ 320	$ 320