Basis of Presentation Reclassification of adjustments out of Accumulated Other Comprehensive Loss (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Natural Gas Swaps	$ (38,379)	$ (77,492)	$ (93,146)	$ (251,357)
Tax Benefit of Natural Gas Swaps	14,025	29,683	36,551	97,760
Natural Gas Swaps, Net of Tax	(24,354)	(47,809)	(56,595)	(153,597)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(8,212)	(13,915)	(24,635)	(39,937)
Defined Benefit Plan, Amortization of Gains (Losses)	21,055	26,611	69,802	79,688
Other Comprehensive Income (Loss), Finalization of Pension and Non-Pension Postretirement Plan Valuation, Net of Tax	6,296		(38,498)
Defined Benefit Plan, Net Periodic Benefit Cost	19,139	12,696	83,665	39,751
Tax Expense on Actuarially Determined Long-Term Liabilities	7,306	4,775	(31,936)	(14,946)
Actuarially Determined Long-Term Liability Adjustments, Net of Tax	11,833	7,921	51,729	24,805
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(408)	(408)	(1,223)	(1,223)
Defined Benefit Plan, Amortization of Gains (Losses)	(8,042)	(11,959)	(30,764)	(35,876)
Other Comprehensive Income (Loss), Finalization of Pension and Non-Pension Postretirement Plan Valuation, Net of Tax	6,296	0	38,498	0
Defined Benefit Plan, Net Periodic Benefit Cost	$ 14,988	$ 14,936	$ 73,281	$ 43,756