Amount of Financial Security Plan Benefit Expense Charged to Costs and Expenses (Detail) (Financial Security Defined Benefit Plans, USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010
Financial Security Defined Benefit Plans
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Service cost	$ 2,147	$ 2,213	$ 1,673
Interest cost	2,517	2,311	2,289
Recognized actuarial loss	4,366	2,347	3,854
Recognized actuarial loss adjustment			4,441
Defined benefit pension plan, total	$ 9,030	$ 6,871	$ 12,257