Employee Benefit and Retirement Plans (Narrative) (Details) $ in Thousands	12 Months Ended
	Apr. 30, 2020 USD ($) plan	Apr. 30, 2019 USD ($)	Apr. 30, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Recognized expenses for profit-sharing contributions	$ 3,700	$ 3,800	$ 3,700
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	$ 68,600
Accumulated other comprehensive loss, net of tax	51,173	49,491
Expected recognized net actuarial losses in net periodic pension benefit cost, before tax	1,800
Expected recognized net actuarial losses in net periodic pension benefit cost, after tax	1,300
Accumulated benefit obligation	191,200	168,800
Company contributions	$ 469	$ 7,283
Plan asset actual allocation	100.00%	100.00%
Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan asset actual allocation	33.00%	31.00%
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%
401(k) Plan [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
401(k) contributions, percent match of employee's annual contribution	4.00%
Eligibility period	60 days
Expense for 401(k) matching contributions	$ 10,100	$ 9,900	$ 8,000
Maximum annual contribution per employee (as a percent)	3.00%
Annually escalated percent, beginning January 1, 2021	1.00%
Maximum escalated percent	8.00%
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Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, minimum age requirement	18 years
Defined contribution plan, minimum consecutive months employed requirement	6 months