Components of Net Periodic Pension Cost for Defined Benefit Plan and Defined Contribution Plans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010
Employee Benefit Plan [Line Items]
Service cost		$ 575	$ 490
Interest cost	1,213	1,140	1,059
Actual return on plan assets	(789)	3,921	3,152
Net amortization and deferral	(756)	(4,825)	(3,811)
Net periodic pension cost (benefit) on defined benefit plan	(332)	811	890
Defined contribution plans	8,643	9,870	8,817
Total retirement plan cost	$ 8,311	$ 10,681	$ 9,707