Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivative [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	$ 4,208	$ 282	$ 3,957
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	16,438	(2,367)	(69,235)
Coal Purchases [Member]
Derivative [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	(2,009)	5,145	1,089
Gains (Losses) Reclassified from OCI into Income (Effective Portion)		(1,202)	(13,181)
Coal Sales [Member]
Derivative [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	4,923	(4,714)	(7,441)
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	1,572	(1,602)	(6,999)
Coal [Member] \| Change In Fair Value Of Coal Derivatives And Coal Trading Activities Net [Member]
Derivative [Line Items]
Derivatives Not Designated as Hedging Instruments, Gains (Losses), Unrealized	6,438	(10,991)	9,673
Gain on Derivatives Used in Fair Value Hedge Relationships			2,586
Coal [Member] \| Other Operating Income, Net [Member]
Derivative [Line Items]
Derivatives Not Designated as Hedging Instruments, Gain, Realized		4,542
Derivatives Not Designated as Hedging Instruments, Losses, Realized	(7)
Heating Oil - Diesel Purchases [Member]
Derivative [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	1,294	(149)	10,309
Heating Oil - Diesel Purchases [Member] \| Coal Purchases [Member]
Derivative [Line Items]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	14,866	437	(49,055)
Heating Oil - Fuel Surcharges [Member] \| Other Operating Income, Net [Member]
Derivative [Line Items]
Derivatives Not Designated as Hedging Instruments, Gains (Losses), Unrealized	(2,906)
Firm Commitments [Member] \| Change In Fair Value Of Coal Derivatives And Coal Trading Activities Net [Member]
Derivative [Line Items]
Loss on Hedged Items in Fair Value Hedge Relationships			$ (2,586)

The amount of net gains or losses on a cash flow hedge reclassified to revenues from accumulated other comprehensive income.

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The amount recognized in earnings related to the change in fair value during the period of derivative or nonderivative instruments designated as fair value hedging instruments.

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The amount recognized in earnings related to the change in fair value during the period of the hedged item in a fair value hedge.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

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Gain included in earnings for the period from the change in fair value of derivative instruments not designated as hedging instruments.

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Net gain (loss) from the increase (decrease) in fair value of derivative instrument not designated as hedging instrument.

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Loss included in earnings for the period from the change in fair value of derivative instruments not designated as hedging instruments.

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