Components of Net Periodic Benefit Costs (Detail) (Deferred Compensation Plan, USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2014	Jan. 31, 2013
Deferred Compensation Plan
Defined Benefit Plan Disclosure [Line Items]
Amortization of actuarial loss	$ 780	$ 594	$ 2,339	$ 1,782
Interest cost	675	756	2,027	2,268
Net periodic benefit costs	$ 1,455	$ 1,350	$ 4,366	$ 4,050