Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Document Fiscal Year Focus			2013
Gain (Loss) Recognized in OCI (Effective Portion)	$ (35)	$ 1,489	$ (393)	[1]	$ 3,780	[1]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	541	809	1,401	[1]	1,010	[1]
Coal Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	613	(742)	431	[1]	(944)	[1]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	(148)	0	(510)	[1]		[1]
Coal Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	(648)	2,231	(824)	[2]	4,724	[2]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	689	809	1,911	[2]	1,010	[2]
Coal [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	4,109	27,446	5,579	[3]	34,998	[3]
Coal derivative settlements, non-hedging	6,579	8,671	15,796	[4]	11,829	[4]
Heating Oil-Diesel Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)	(5,211)	(22,509)	(9,472)	[4]	(22,086)	[4]
Heating Oil-Fuel Surchages [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)	$ (30)	$ (2,599)	$ (595)	[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