Summary of Long-term Debt and Short-term Borrowings Outstanding (Detail) - USD ($) $ in Thousands	May. 31, 2015	May. 31, 2014
Debt Instrument [Line Items]
Debt	$ 670,743	$ 666,325
current maturities and short-term borrowings	91,391	111,535
Total long-term debt	579,352	554,790
Short-term borrowings
Debt Instrument [Line Items]
Debt	90,550	10,362
Floating rate senior notes due December 17, 2014
Debt Instrument [Line Items]
Debt		100,000
6.50% senior notes due April 15, 2020
Debt Instrument [Line Items]
Debt	149,920	149,912
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	249,524	249,472
Industrial revenue bonds due April 2019
Debt Instrument [Line Items]
Debt		2,024
Term Loan
Debt Instrument [Line Items]
Debt	30,429	4,235
Other Debt
Debt Instrument [Line Items]
Debt	$ 320	$ 320