Accumulated Other Comprehensive Income (Schedule of Reclassifications) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	$ 735,971	$ 737,370
Benefit from income taxes	43,611	59,353
Net loss	(124,139)	(70,049)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	303	859
Benefit from income taxes	(109)	(309)
Net loss	194	550
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	2,626	2,908
Amortization of actuarial gains (losses), net	(779)	(4,862)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax	1,847	(1,954)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax, Portion Attributable to Parent	(665)	703
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax, Portion Attributable to Parent	1,182	(1,251)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and investment income	(556)	(59)
Benefit from income taxes	200	21
Net loss	$ (356)	$ (38)