Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,768	$ 2,166
Interest cost	4,286	5,791
Expected return on plan assets	(6,133)	(6,344)
Amortization of prior service cost (credit)	156	183
Recognized actuarial loss	5,279	4,269
Net periodic benefit expense	5,356	6,065
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	326	447
Interest cost	521	794
Expected return on plan assets	0	0
Amortization of prior service cost (credit)	0	0
Recognized actuarial loss	(7)	0
Net periodic benefit expense	$ 840	$ 1,241