Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,062	$ 2,255
Interest cost	7,151	6,737
Expected return on plan assets	(6,460)	(7,506)
Amortization of prior service cost (credit)	247	257
Recognized actuarial loss	3,514	5,215
Net periodic benefit expense	6,514	6,958
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	420	494
Interest cost	945	874
Amortization of prior service cost (credit)	(98)	(10)
Net periodic benefit expense	$ 1,267	$ 1,358