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Defined Benefit Pension Plans - Pension Expenses (Detail) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jan. 31, 2020
Jan. 31, 2019
Jan. 31, 2020
Jan. 31, 2019
Retirement Benefits [Abstract]        
Service cost $ 0 $ 0 $ 0 $ 0
Interest cost 208 214 624 644
Expected return on plan assets (355) (362) (1,065) (1,086)
Recognition of net loss 260 221 780 663
Net periodic pension expense $ 113 $ 73 $ 339 $ 221