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Defined Benefit Pension Plans - Pension Expenses (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Oct. 31, 2020
Oct. 31, 2019
Oct. 31, 2020
Oct. 31, 2019
Retirement Benefits [Abstract]        
Service cost $ 0 $ 0 $ 0 $ 0
Interest cost 181 208 362 416
Expected return on plan assets (321) (355) (642) (710)
Recognition of net loss 429 260 857 520
Net periodic pension expense $ 289 $ 113 $ 577 $ 226