Employee Benefit and Retirement Plans (Narrative) (Details) $ in Thousands		12 Months Ended
	Dec. 31, 2020 USD ($)	Apr. 30, 2021 USD ($) plan	Apr. 30, 2020 USD ($)	Apr. 30, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Recognized expenses for profit-sharing contributions		$ 2,900	$ 3,700	$ 3,800
401(k) contributions, percent match of employee's annual contribution				100.00%
Effective maximum contribution of base earnings				4.00%
Number of defined benefit pension plans | plan		2
Accumulated other comprehensive loss		$ 73,100
Accumulated other comprehensive loss, net of tax		54,568	51,173
Expected recognized net actuarial losses in net periodic pension benefit cost, before tax		1,200
Expected recognized net actuarial losses in net periodic pension benefit cost, after tax		900
Accumulated benefit obligation		196,500	191,200
Company contributions		$ 0	$ 469
Plan asset actual allocation		100.00%	100.00%
Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan asset actual allocation		0.00%	33.00%
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Percent of after tax earnings contributed in profit sharing		0.00%
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Percent of after tax earnings contributed in profit sharing		5.00%
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, estimated termination cost	$ 1,600
401(k) Plan [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expense for 401(k) matching contributions		$ 11,900	$ 10,100	$ 9,900
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Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, minimum age requirement		18 years