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Defined Benefit Pension Plans - Pension Expenses (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Jan. 31, 2019
Jan. 31, 2018
Jan. 31, 2019
Jan. 31, 2018
Retirement Benefits [Abstract]        
Service cost $ 0 $ 0 $ 0 $ 0
Interest cost 214 219 644 657
Expected return on plan assets (362) (328) (1,086) (984)
Recognition of net loss 221 283 663 849
Net periodic pension expense $ 73 $ 174 $ 221 $ 522