Derivatives (Disclosure Of Fair Value Of Derivatives) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	$ (136,148)	$ (98,686)
Derivative Liability, Fair Value, Gross Asset	136,148	98,686
Derivative Asset	18,856us-gaap_DerivativeAssets	13,557us-gaap_DerivativeAssets
Derivative Liability	(1,010)us-gaap_DerivativeLiabilities	(766)us-gaap_DerivativeLiabilities
Net derivatives as classified in the balance sheet	17,846	12,791
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Price Risk Derivative Instruments Not Designated as Hedging Instruments Asset, at Fair Value	148,108	105,708
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value	(137,051)	(96,960)
Not Designated as Hedging Instrument [Member] \| Coal Contract [Member]
Derivative [Line Items]
Derivative Assets	126,397	96,898
Derivative Liabilities	(125,204)	(93,272)
Heating Oil-Diesel Purchases [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Price Risk Derivative Instruments Not Designated as Hedging Instruments Asset, at Fair Value	4,079	300
Coal Contract [Member] \| Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Assets	6,896	6,535
Derivative Liabilities	(107)	(2,492)
Coal Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Price Risk Derivative Instruments Not Designated as Hedging Instruments Asset, at Fair Value	16,484	8,510
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value	(11,094)	(3,688)
Natural Gas [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Price Risk Derivative Instruments Not Designated as Hedging Instruments Asset, at Fair Value	1,148	0
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value	(753)	0
Price Risk Derivative [Member]
Derivative [Line Items]
Derivative Assets	155,004	112,243
Derivative Liabilities	$ (137,158)	$ (99,452)

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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