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Retirement Benefits - Summary of Components of Net Periodic Pension Cost (Detail) - USD ($)
$ in Thousands
12 Months Ended
Apr. 30, 2021
Apr. 30, 2020
Retirement Benefits [Abstract]    
Interest cost $ 723 $ 832
Expected return on plan assets (1,284) (1,421)
Recognition of net loss 1,714 1,043
Net periodic pension expense $ 1,153 $ 454