Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) (USD $) In Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Gain (Loss) Recognized in OCI (Effective Portion)	$ (5,840)	$ 2,017	$ 4,052	$ (6,112)
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	5,588	(999)	15,736	(2,969)
Gain (Loss) Recognized in Income (Ineffective Portion and Amount Excluded from Effectiveness Testing)
Coal [Member] \| Change In Fair Value Of Coal Derivatives And Coal Trading Activities Net [Member]
Derivatives Not Designated as Hedging Instruments, Losses, Unrealized	(6,131)	(993)	(7,550)	(9,381)
Coal [Member] \| Other Operating Income, Net [Member]
Derivatives Not Designated as Hedging Instruments, Gain, Realized	166	1,079	313	3,931
Heating Oil-diesel purchases [Member]
Gain (Loss) Recognized in OCI (Effective Portion)	(6,386)	3,052	1,535	(5,508)
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	5,122	93	14,946	(211)
Gain (Loss) Recognized in Income (Ineffective Portion and Amount Excluded from Effectiveness Testing)
Heating oil-fuel surchages [Member] \| Other Operating Income, Net [Member]
Derivatives Not Designated as Hedging Instruments, Losses, Unrealized	(2,501)		(2,501)
Coal Purchases [Member]
Gain (Loss) Recognized in OCI (Effective Portion)	(1,274)	(2,535)	(2,053)	5,534
Gains (Losses) Reclassified from OCI into Income (Effective Portion)		(866)		(1,202)
Gain (Loss) Recognized in Income (Ineffective Portion and Amount Excluded from Effectiveness Testing)
Coal Sales [Member]
Gain (Loss) Recognized in OCI (Effective Portion)	1,820	1,500	4,570	(6,138)
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	466	(226)	790	(1,556)
Gain (Loss) Recognized in Income (Ineffective Portion and Amount Excluded from Effectiveness Testing)

The amount of net gains or losses on a cash flow hedge reclassified in the period to cost of sales from accumulated other comprehensive income.

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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 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 portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

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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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