Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,610	$ 5,898	$ 8,533	$ 15,751
Interest cost	5,913	8,972	20,386	24,893
Expected return on plan assets	(6,626)	(10,471)	(21,709)	(27,882)
Amortization of prior service cost	323	187	963	580
Amortization of transitional asset		402		947
Recognized actuarial loss	3,617	3,885	10,864	11,667
Gross periodic benefit expense			19,037	25,956
Special termination benefits				8,606
Curtailments			822	306
Net periodic benefit expense	5,837	8,873	19,859	34,868
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	674	826	2,022	2,482
Interest cost	1,109	1,192	3,324	3,576
Amortization of prior service cost	(21)	(21)	(62)	(62)
Amortization of transitional asset	2	2	4	5
Recognized actuarial loss	38	193	113	578
Gross periodic benefit expense			5,401	6,579
Special termination benefits			(19)
Net periodic benefit expense	$ 1,802	$ 2,192	$ 5,382	$ 6,579