Pretax Amounts in Accumulated Other Comprehensive Loss Expected to be Recognized as Comprehensive of Net Periodic Postretirement Benefit Cost (Credit) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2012
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 2,927
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year, Total	2,927
Other Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	515
Prior service credit	(775)
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year, Total	$ (260)