Quarterly report pursuant to Section 13 or 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
3 Months Ended
Jul. 31, 2015
Jul. 31, 2014
Defined Benefit Plan Disclosure [Line Items]    
Amortization of actuarial loss $ 731 $ 763
Interest cost 703 747
Net periodic benefit costs $ 1,434 $ 1,510