Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,768	$ 2,166	$ 3,536	$ 4,332
Interest cost	4,300	5,763	8,586	11,554
Expected return on plan assets	(6,155)	(6,297)	(12,288)	(12,641)
Amortization of prior service cost (credit)	156	183	312	366
Recognized actuarial loss	5,281	4,264	10,560	8,533
Net periodic benefit expense	5,350	6,079	10,706	12,144
Other - curtailment	0	586	0	586
Other - special termination benefits	0	8,435	0	8,435
Net periodic benefit expense	5,350	15,100	10,706	21,165
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	327	446	653	893
Interest cost	521	794	1,042	1,588
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (credit)	0	0	0	0
Recognized actuarial loss	(8)	0	(15)	0
Net periodic benefit expense	840	1,240	1,680	2,481
Other - curtailment	0	(1,825)	0	(1,825)
Other - special termination benefits	0	0	0	0
Net periodic benefit expense	$ 840	$ (585)	$ 1,680	$ 656