Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4,772	$ 6,284	$ 9,853	$ 12,840
Interest cost	7,971	8,253	15,921	16,468
Expected return on plan assets	(8,724)	(8,528)	(17,411)	(17,008)
Amortization of prior service cost	198	228	393	453
Amortization of transitional asset	274	212	545	420
Recognized actuarial loss	3,891	1,733	7,782	3,466
Defined Benefit Plan, Gross Periodic Benefit Cost, Total	8,382	8,182	17,083	16,639
Special termination benefits	8,606		8,606
Curtailments	306		306
Net periodic benefit expense	17,294	8,182	25,995	16,639
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	828	672	1,656	1,344
Interest cost	1,192	1,277	2,384	2,555
Amortization of prior service cost	(20)	(20)	(41)	(41)
Amortization of transitional asset	3	2	3	3
Recognized actuarial loss	190	59	385	118
Defined Benefit Plan, Gross Periodic Benefit Cost, Total	2,193	1,990	4,387	3,979
Net periodic benefit expense	$ 2,193	$ 1,990	$ 4,387	$ 3,979