Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,166	$ 2,062	$ 4,332	$ 4,124
Interest cost	5,763	7,100	11,554	14,251
Expected return on plan assets	(6,297)	(6,370)	(12,641)	(12,830)
Amortization of prior service cost (credit)	183	246	366	493
Recognized actuarial loss	4,264	3,508	8,533	7,022
Net periodic benefit expense	6,079	6,546	12,144	13,060
Other - curtailment	586	0	586	0
Other - special termination benefits	8,435	0	8,435	0
Total net periodic benefit expense	15,100	6,546	21,165	13,060
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	446	420	893	840
Interest cost	794	943	1,588	1,888
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (credit)	0	(97)	0	(195)
Recognized actuarial loss	0	0	0	0
Net periodic benefit expense	1,240	1,266	2,481	2,533
Other - curtailment	(1,825)	0	(1,825)	0
Other - special termination benefits	0	0	0	0
Total net periodic benefit expense	$ (585)	$ 1,266	$ 656	$ 2,533