Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,064	$ 2,252	$ 6,188	$ 6,761
Interest cost	7,151	6,716	21,402	20,160
Expected return on plan assets	(6,455)	(7,476)	(19,285)	(22,435)
Amortization of prior service cost (credit)	248	254	741	767
Recognized actuarial loss	3,516	5,197	10,538	15,593
Net periodic benefit expense	6,524	6,943	19,584	20,846
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	421	492	1,261	1,479
Interest cost	945	874	2,833	2,622
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (credit)	(98)	(10)	(293)	(29)
Recognized actuarial loss	0	0	0	0
Net periodic benefit expense	$ 1,268	$ 1,356	$ 3,801	$ 4,072