Accumulated Other Comprehensive Income (Schedule of Reclassifications) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	$ 688,544	$ 742,180	$ 2,010,011	$ 2,191,927
Benefit from income taxes	343,865	34,350	351,332	112,830
Net loss	(1,999,476)	(97,218)	(2,280,774)	(318,217)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	3,598	892	6,806	1,346
Benefit from income taxes	(1,295)	(321)	(2,452)	(485)
Net loss	2,303	571	4,354	861
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	1,759	6,250	6,976
Amortization of actuarial gains (losses), net	(3,266)	(550)	(11,200)	(1,650)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax	(1,183)	1,209	(4,950)	5,326
Benefit from income taxes	426	(435)	1,782	(1,917)
Net of tax	(757)	774	(3,168)	3,409
Reclassification out of Accumulated Other Comprehensive Income [Member] | Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Benefit from income taxes	358	53	1,914	657
Net loss	(723)	(92)	(3,394)	(1,167)
Interest and investment income	$ (1,081)	$ (145)	$ (5,308)	$ (1,824)