Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	$ 81		$ (5,840)		$ 3,861		$ 4,052
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	542		5,588		1,552		15,736
Coal Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	(178)	[1]	(1,274)	[1]	(1,122)	[1]	(2,053)	[1]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)		[1]		[1]		[1]		[1]
Coal Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	259	[2]	1,820	[2]	4,983	[2]	4,570	[2]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	542	[2]	466	[2]	1,552	[2]	790	[2]
Heating Oil-Diesel Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)		[1]	(6,386)	[1]		[1]	1,535	[1]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)		[1]	5,122	[1]		[1]	14,946	[1]
Not Designated as Hedging Instrument [Member] | Coal [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	(11,328)	[3]	(6,131)	[3]	23,670	[3]	(7,550)	[3]
Realized Gains (Losses)	14,072	[4]	166	[4]	25,901	[4]	313	[4]
Not Designated as Hedging Instrument [Member] | Heating Oil-Diesel Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)	5,184	[4]		[4]	(16,902)	[4]		[4]
Not Designated as Hedging Instrument [Member] | Heating Oil-Fuel Surchages [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)	$ 1,092	[4]	$ (2,501)	[4]	$ (1,140)	[4]	$ (2,501)	[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