Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,153	$ 5,081
Interest cost	5,608	7,950
Expected return on plan assets	(5,385)	(8,687)
Amortization of prior service cost	319	195
Amortization of transitional asset		271
Recognized actuarial loss	3,529	3,891
Curtailments	822
Net periodic benefit expense	8,046	8,701
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	673	828
Interest cost	1,108	1,192
Amortization of prior service cost	(21)	(21)
Recognized actuarial loss	39	195
Curtailments	(19)
Net periodic benefit expense	$ 1,780	$ 2,194