Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	$ (358)		$ 2,291
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	859		201
Coal Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	(182)	[1]	(202)	[1]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	(362)	[1]		[1]
Coal Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	(176)	[2]	2,493	[2]
Gains (Losses) Reclassified from OCI into Income (Effective Portion)	1,221	[2]	201	[2]
Coal [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	1,470	[3]	7,552	[3]
Coal derivative settlements, non-hedging	9,217	[4]	3,158	[4]
Heating Oil-Diesel Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)	(4,261)	[4]	423	[4]
Heating Oil-Fuel Surchages [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)	$ (565)	[4]	$ 367	[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