Accumulated Other Comprehensive Income (Schedule of Reclassifications) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	$ 742,180	$ 791,269	$ 2,191,927	$ 2,294,971
Benefit from income taxes	34,350	121,913	112,830	230,734
Net loss	(97,218)	(128,363)	(318,217)	(270,618)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	892	692	1,346	2,093
Benefit from income taxes	(321)	(249)	(485)	(754)
Net loss	571	443	861	1,339
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 (1)	1,759	5,573	6,976	11,154
Amortization of actuarial gains (losses), net (1)	(550)	(3,823)	(1,650)	(13,108)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax	1,209	1,750	5,326	(1,954)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Tax Portion	(435)	(631)	(1,917)	702
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax, Portion Attributable to Parent	774	1,119	3,409	(1,252)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and investment income	(145)	(4)	(1,824)	(313)
Benefit from income taxes	53	2	657	113
Net loss	$ (92)	$ (2)	$ (1,167)	$ (200)