Components of Net Periodic Benefit Costs (Detail) (Deferred Compensation Plan, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jul. 31, 2014	Jul. 31, 2013
Deferred Compensation Plan
Defined Benefit Plan Disclosure [Line Items]
Amortization of actuarial loss	$ 763	$ 780
Interest cost	747	676
Net periodic benefit costs	$ 1,510	$ 1,456