Retirement Plans - Pretax Amounts in Accumulated Other Comprehensive Loss Expected to be Recognized as Components of Net Periodic Postretirement Benefit Cost (Credit) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2013
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 615
Total amounts expected to be recognized in OCL as components of net periodic postretirement benefit cost	615
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	229
Prior service credit	(775)
Total amounts expected to be recognized in OCL as components of net periodic postretirement benefit cost	$ (546)