Amount of Financial Security Plan Benefit Expense Charged to Costs and Expenses (Detail) (Financial Security Defined Benefit Plans, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Aug. 31, 2013	Aug. 31, 2012
Financial Security Defined Benefit Plans
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Service cost	$ 536	$ 593
Interest cost	609	591
Defined benefit pension plan, total	$ 1,145	$ 1,184