Annual report pursuant to Section 13 and 15(d)

Components of Net Periodic Benefit Costs (Detail)

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Components of Net Periodic Benefit Costs (Detail) (Deferred Compensation Plan, USD $)
In Thousands, unless otherwise specified
12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Apr. 30, 2011
Deferred Compensation Plan
     
Defined Benefit Plan Disclosure [Line Items]      
Service cost     $ 137
Interest cost 2,868 3,346 3,495
Amortization of actuarial loss 2,357 1,374 422
Net periodic benefit cost $ 5,225 $ 4,720 $ 4,054