Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,664	$ 2,064	$ 5,996	$ 6,188
Interest cost	4,827	7,151	16,381	21,402
Expected return on plan assets	(5,773)	(6,455)	(18,414)	(19,285)
Amortization of prior service cost (credit)	149	248	515	741
Recognized actuarial loss	5,690	3,516	14,223	10,538
Net periodic benefit expense	6,557	6,524	18,701	19,584
Other - curtailment			586	0
Other - special termination benefits			8,435	0
Total net periodic benefit expense			27,722	19,584
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	342	421	1,235	1,261
Interest cost	612	945	2,200	2,833
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (credit)	0	(98)	0	(293)
Recognized actuarial loss	(24)	0	(24)	0
Net periodic benefit expense	$ 930	$ 1,268	3,411	3,801
Other - curtailment			(1,825)	0
Other - special termination benefits			0	0
Total net periodic benefit expense			$ 1,586	$ 3,801