Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,770	$ 4,772	$ 5,923	$ 9,853
Interest cost	8,865	7,971	14,473	15,921
Expected return on plan assets	(9,698)	(8,724)	(15,083)	(17,411)
Amortization of prior service cost	321	198	640	393
Amortization of transitional asset		274		545
Recognized actuarial loss	3,718	3,891	7,247	7,782
Gross periodic benefit expense	5,976	8,382	13,200	17,083
Special termination benefits		8,606		8,606
Curtailments		306	822	306
Net periodic benefit expense	5,976	17,294	14,022	25,995
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	675	828	1,348	1,656
Interest cost	1,107	1,192	2,215	2,384
Amortization of prior service cost	(20)	(20)	(41)	(41)
Amortization of transitional asset	2	3	2	3
Recognized actuarial loss	36	190	75	385
Gross periodic benefit expense	1,800	2,193	3,599	4,387
Curtailments			(19)
Net periodic benefit expense	$ 1,800	$ 2,193	$ 3,580	$ 4,387