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Defined Benefit Pension Plans - Pension Expenses (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Jan. 31, 2018
Jan. 31, 2017
Jan. 31, 2018
Jan. 31, 2017
Retirement Benefits [Abstract]        
Service cost $ 0 $ 0 $ 0 $ 0
Interest cost 219 232 687 695
Expected return on plan assets (328) (311) (984) (932)
Recognition of net loss 283 314 849 942
Net periodic pension expense $ 174 $ 235 $ 522 $ 705