Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncome [Line Items]
Total amounts reclassified from accumulated other comprehensive income, net	$ (58,259)		$ (131,547)
Reclassification out of Accumulated Other Comprehensive Income
ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncome [Line Items]
Plan settlement	477		477
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax		$ 0		$ 0
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncome [Line Items]
Total reclassified from accumulated other comprehensive income	19,461		$ 85,566
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent | Minimum
ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncome [Line Items]
Actuarial loss, amortization period			7 months 24 days
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent | Maximum
ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncome [Line Items]
Actuarial loss, amortization period			11 years 5 months 19 days
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncome [Line Items]
Total reclassified from accumulated other comprehensive income	(89,861)		$ (267,658)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent | Minimum
ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncome [Line Items]
Unrecognized prior service credit, amortization period			10 months 13 days
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent | Maximum
ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncome [Line Items]
Unrecognized prior service credit, amortization period			23 years 10 months 28 days
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment Attributable to Parent
ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncome [Line Items]
Total reclassified from accumulated other comprehensive income	(69,923)		$ (181,615)
Tax benefit	11,297		48,974
Total amounts reclassified from accumulated other comprehensive income, net	(58,626)		(132,641)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncome [Line Items]
Tax benefit	(248)		(737)
Total amounts reclassified from accumulated other comprehensive income, net	367		1,094
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	$ (615)		$ (1,831)