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Defined Benefit Pension Plans - Pension Expenses (Detail) - USD ($)
$ in Thousands
3 Months Ended
Jul. 31, 2018
Jul. 31, 2017
Retirement Benefits [Abstract]    
Service cost $ 0 $ 0
Interest cost 215 219
Expected return on plan assets (362) (339)
Recognition of net loss 221 283
Net periodic pension expense $ 74 $ 163