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Retirement Plans (Details) - USD ($)
$ in Thousands
 3 Months Ended
Jul. 31, 2021
Jul. 31, 2020
Components of net pension income for defined benefit plans [Abstract]    
Service cost $ 307 $ 333
Interest cost 5,223 4,521
Expected return on plan assets (10,259) (9,378)
Amortization of prior service cost (22) (25)
Amortization of net actuarial loss 1,897 1,987
Net pension income (2,854) (2,562)
Employer defined benefit pension plan contributions 4,500 5,100
Defined Contribution Savings Plans [Abstract]    
Expense for employer defined contribution savings plans $ 9,100 $ 6,600