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Defined Benefit Pension Plans - Pension Expenses (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Oct. 31, 2019
Oct. 31, 2018
Oct. 31, 2019
Oct. 31, 2018
Retirement Benefits [Abstract]        
Service cost $ 0 $ 0 $ 0 $ 0
Interest cost 208 215 416 430
Expected return on plan assets (355) (362) (710) (724)
Recognition of net loss 260 221 520 442
Net periodic pension expense $ 113 $ 74 $ 226 $ 148