Employee Benefit Plans (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 9	$ 21,478	$ 27,065
Interest cost	14,604	17,070	16,207
Curtailments	0	(25,368)	47
Settlements	2,656	646	0
Expected return on plan assets	(20,367)	(23,756)	(23,761)
Amortization of prior service credits	0	(257)	(204)
Amortization of other actuarial losses	8,850	3,128	14,616
Total net benefit	5,752	(7,059)	33,970
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	866	1,649	2,027
Interest cost	1,904	1,841	1,739
Curtailments		0	(5,444)
Settlements	0	0	0
Expected return on plan assets	0	0	0
Amortization of prior service credits	(8,335)	(10,003)	(10,621)
Amortization of other actuarial losses	(2,109)	(761)	(252)
Total net benefit	$ (7,674)	$ (7,274)	$ (12,551)