Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	$ 1,489		$ (4,896)		$ 3,780		$ 9,892
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	809		6,891		1,010		10,148
Coal Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	(742)	[1]	97	[1]	(944)	[1]	(779)	[1]
Coal Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	2,231	[2]	1,344	[2]	4,724	[2]	2,750	[2]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	809	[2]	237	[2]	1,010	[2]	324	[2]
Heating Oil-Diesel Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)			(6,337)	[1]			7,921	[1]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)			6,654	[1]			9,824	[1]
Not Designated as Hedging Instrument [Member] | Coal [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	27,446	[3]	(374)	[3]	34,998	[3]	(1,419)	[3]
Realized Gains (Losses)	8,671	[4]	147	[4]	11,829	[4]	147	[4]
Not Designated as Hedging Instrument [Member] | Heating Oil-Diesel Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)	(22,509)	[4]			(22,086)	[4]
Not Designated as Hedging Instrument [Member] | Heating Oil-Fuel Surchages [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)	$ (2,599)	[4]			$ (2,232)	[4]

[1] Cost of sales

[2] Revenues

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

[4] Other operating income, net