Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 8,136	$ 17,948	$ 22,470
Interest cost	25,185	33,168	33,680
Expected return on plan assets	(28,154)	(34,016)	(33,723)
Amortization of prior service cost (credit)	1,204	1,560	899
Amortization of transitional (asset) liability		(1)	(480)
Recognized actuarial loss	16,165	15,147	9,471
Gross periodic benefit expense	22,536	33,806	32,317
Termination benefits expense		8,606
Curtailment expense	822	306
Net periodic benefit expense	23,358	42,718	32,317
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,864	3,180	2,459
Interest cost	3,800	4,883	4,617
Amortization of prior service cost (credit)	(75)	(82)	(82)
Recognized actuarial loss	5	992	5
Gross periodic benefit expense	5,594	8,973	6,999
Curtailment expense	(19)
Net periodic benefit expense	$ 5,575	$ 8,973	$ 6,999