Basis of Presentation Reclassification of adjustments out of Accumulated Other Comprehensive Loss (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Natural Gas Swaps	$ (34,697)	$ (79,321)
Tax Benefit of Natural Gas Swaps	11,984	31,380
Natural Gas Swaps, Net of Tax	(22,713)	(47,941)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(8,212)	(12,106)
Defined Benefit Plan, Amortization of Gains (Losses)	25,188	27,005
Other Comprehensive Income (Loss), Finalization of Pension and Non-Pension Postretirement Plan Valuation, Net of Tax	27,115
Defined Benefit Plan, Net Periodic Benefit Cost	44,091	14,899
Tax Expense on Actuarially Determined Long-Term Liabilities	16,831	5,602
Actuarially Determined Long-Term Liability Adjustments, Net of Tax	27,260	9,297
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(408)	(408)
Defined Benefit Plan, Amortization of Gains (Losses)	(12,175)	(12,263)
Other Comprehensive Income (Loss), Finalization of Pension and Non-Pension Postretirement Plan Valuation, Net of Tax	27,115	0
Defined Benefit Plan, Net Periodic Benefit Cost	$ 41,287	$ 14,759