Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,062	$ 2,254	$ 4,124	$ 4,509
Interest cost	7,100	6,707	14,251	13,444
Expected return on plan assets	(6,370)	(7,453)	(12,830)	(14,959)
Amortization of prior service cost (credit)	246	256	493	513
Recognized actuarial loss	3,508	5,181	7,022	10,396
Net periodic benefit expense	6,546	6,945	13,060	13,903
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	420	493	840	987
Interest cost	943	874	1,888	1,748
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (credit)	(97)	(9)	(195)	(19)
Recognized actuarial loss	0	0	0	0
Net periodic benefit expense	$ 1,266	$ 1,358	$ 2,533	$ 2,716