Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 8,994	$ 8,279	$ 8,136
Interest cost	26,168	27,047	25,185
Expected return on plan assets	(29,236)	(28,941)	(28,154)
Amortization of prior service cost (credit)	1,021	1,026	1,204
Recognized actuarial loss	21,893	16,691	16,165
Gross periodic benefit expense	28,840	24,102	22,536
Curtailment expense			822
Net periodic benefit expense	28,840	24,102	23,358
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,965	1,601	1,864
Interest cost	3,427	3,444	3,800
Amortization of prior service cost (credit)	(38)	(74)	(75)
Recognized actuarial loss			5
Gross periodic benefit expense	5,354	4,971	5,594
Curtailment expense			(19)
Net periodic benefit expense	$ 5,354	$ 4,971	$ 5,575