v2.4.0.8
Basis of Presentation Reclassification of adjustments out of Accumulated Other Comprehensive Loss (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Natural Gas Swaps $ (20,070) $ (94,544) $ (54,767) $ (173,865)
Tax Benefit of Natural Gas Swaps 10,542 36,697 22,526 68,077
Natural Gas Swaps, Net of Tax (9,528) (57,847) (32,241) (105,788)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit) (8,211) (13,915) (16,423) (26,021)
Defined Benefit Plan, Amortization of Gains (Losses) 23,559 26,072 48,747 53,077
Other Comprehensive Income (Loss), Finalization of Pension and Non-Pension Postretirement Plan Valuation, Net of Tax 5,087   (32,202)  
Defined Benefit Plan, Net Periodic Benefit Cost 20,435 12,157 64,526 27,056
Tax Expense on Actuarially Determined Long-Term Liabilities 7,800 4,571 (24,631) (10,173)
Actuarially Determined Long-Term Liability Adjustments, Net of Tax 12,635 7,586 39,895 16,883
Pension Plans, Defined Benefit [Member]
        
Defined Benefit Plan, Amortization of Prior Service Cost (Credit) (407) (407) (815) (815)
Defined Benefit Plan, Amortization of Gains (Losses) (10,547) (11,654) (22,722) (23,917)
Other Comprehensive Income (Loss), Finalization of Pension and Non-Pension Postretirement Plan Valuation, Net of Tax 5,087 0 32,202 0
Defined Benefit Plan, Net Periodic Benefit Cost $ 17,006 $ 14,060 $ 58,293 $ 28,819