Accumulated Other Comprehensive Income (Schedule of Reclassifications) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	$ 644,462	$ 713,776	$ 1,321,467	$ 1,449,747
Benefit from income taxes	4,071	34,869	7,467	78,480
Net loss	(168,103)	(96,860)	(281,298)	(220,999)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	2,727	151	3,208	454
Benefit from income taxes	(983)	(55)	(1,157)	(164)
Net loss	1,744	96	2,051	290
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension, Postretirement and Other Postemployment Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of prior service credits	2,083	2,591	4,167	5,217
Amortization of actuarial gains (losses), net	(5,556)	(321)	(7,934)	(1,100)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax	(3,473)	2,270	(3,767)	4,117
Benefit from income taxes	1,251	(817)	1,356	(1,482)
Net of tax	(2,222)	1,453	(2,411)	2,635
Reclassification out of Accumulated Other Comprehensive Income [Member] | Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Benefit from income taxes	549	404	1,556	604
Net loss	(881)	(719)	(2,671)	(1,075)
Interest and investment income	$ (1,430)	$ (1,123)	$ (4,227)	$ (1,679)