Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5,898	$ 6,208	$ 15,751	$ 19,048
Interest cost	8,972	8,239	24,893	24,707
Expected return on plan assets	(10,471)	(8,506)	(27,882)	(25,514)
Amortization of prior service cost	187	227	580	680
Amortization of transitional asset	402	208	947	628
Recognized actuarial loss	3,885	1,735	11,667	5,201
Gross periodic benefit expense			25,956	24,750
Special termination benefits			8,606
Curtailments			306
Net periodic benefit expense	8,873	8,111	34,868	24,750
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	826	672	2,482	2,016
Interest cost	1,192	1,278	3,576	3,833
Amortization of prior service cost	(21)	(20)	(62)	(61)
Amortization of transitional asset	2	1	5	4
Recognized actuarial loss	193	59	578	177
Gross periodic benefit expense			6,579	5,969
Net periodic benefit expense	$ 2,192	$ 1,990	$ 6,579	$ 5,969