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Defined Benefit Pension Plans - Pension Expenses (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 6 Months Ended
Oct. 31, 2013
Oct. 31, 2012
Oct. 31, 2013
Oct. 31, 2012
Compensation And Retirement Disclosure [Abstract]        
Service cost $ 0 $ 0 $ 0 $ 0
Interest cost 217 226 429 453
Expected return on plan assets (324) (305) (641) (607)
Recognition of net loss 288 276 571 551
Net periodic pension expense $ 181 $ 197 $ 359 $ 397