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, 2014	May 31, 2013	May 31, 2012
Employee Benefit Plan [Line Items]
Interest cost	$ 1,403	$ 1,361	$ 1,213
Actual return on plan assets	2,524	4,355	(789)
Net amortization and deferral	(4,175)	(5,522)	(756)
Net periodic pension cost (benefit) on defined benefit plan	(248)	194	(332)
Defined contribution plans	12,586	9,955	8,643
Total retirement plan cost	$ 12,338	$ 10,149	$ 8,311