Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) (USD $) In Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Gain (Loss) Recognized in OCI (Effective Portion)	$ (4,896)		$ (8,642)		$ 9,892		$ (8,129)
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	6,891		724		10,148		(1,970)
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	(374)	[1]	(3,466)	[1]	(1,419)	[1]	(8,388)	[1]
Coal [Member] | Other Operating Income, Net [Member]
Derivatives Not Designated as Hedging Instruments, Gain, Realized	147	[2]	1,252	[2]	147	[2]	2,852	[2]
Heating Oil [Member]
Gain (Loss) Recognized in OCI (Effective Portion)	(6,337)		(8,572)		7,921		(8,560)
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	6,654	[3]	1,925	[3]	9,824	[3]	(304)	[3]
Gain (Loss) Recognized in Income (Ineffective Portion and Amount Excluded from Effectiveness Testing)
Coal Purchases [Member]
Gain (Loss) Recognized in OCI (Effective Portion)	97		7,167		(779)		8,069
Gains (Losses) Reclassified from OCI into Income (Effective Portion)		[3]		[3]		[3]	(336)	[3]
Gain (Loss) Recognized in Income (Ineffective Portion and Amount Excluded from Effectiveness Testing)
Coal Sales [Member]
Gain (Loss) Recognized in OCI (Effective Portion)	1,344		(7,237)		2,750		(7,638)
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	237	[4]	(1,201)	[4]	324	[4]	(1,330)	[4]
Gain (Loss) Recognized in Income (Ineffective Portion and Amount Excluded from Effectiveness Testing)

[1] Change in fair value of coal derivatives and coal trading activities, net

[2] Other operating income, net

[3] Cost of coal sales

[4] Coal sales