Employee Benefit and Retirement Plans (Narrative) (Details) $ in Thousands	12 Months Ended
	Apr. 30, 2018 USD ($) plan	Apr. 30, 2017 USD ($)	Apr. 30, 2016 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Recognized expenses for profit-sharing contributions	$ 3,700	$ 3,600	$ 2,900
401(k) contributions, percent match of employee's annual contribution			100.00%
Effective maximum contribution of base earnings			4.00%
Expense for 401(k) matching contributions
Number of defined benefit pension plans | plan	2
Accumulated other comprehensive loss	$ 66,100
Accumulated other comprehensive loss, net of tax	49,069	40,417
Expected recognized net actuarial losses in net periodic pension benefit cost, before tax	1,600
Expected recognized net actuarial losses in net periodic pension benefit cost, after tax	1,200
Accumulated benefit obligation	163,400	165,200
Expected company contributions to pension plan in 2015	2,300
Company contributions	$ 19,319	$ 27,304
Plan asset actual allocation	100.00%	100.00%
Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan asset actual allocation	60.00%
Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan asset actual allocation	40.00%	57.00%
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%
Expense for 401(k) matching contributions	$ 8,000	$ 7,200	$ 6,600
Eligibility period	60 days
Maximum annual contribution per employee (as a percent)	60.00%
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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