Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,166	$ 2,062
Interest cost	5,791	7,151
Expected return on plan assets	(6,344)	(6,460)
Amortization of prior service cost (credit)	183	247
Recognized actuarial loss	4,269	3,514
Net periodic benefit expense	6,065	6,514
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	447	420
Interest cost	794	945
Expected return on plan assets	0	0
Amortization of prior service cost (credit)	0	(98)
Recognized actuarial loss	0	0
Net periodic benefit expense	$ 1,241	$ 1,267