Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	$ 1,408	$ 2,190	$ 2,644	$ 1,797
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion	892	1,034	1,346	2,189
Designated as Hedging Instrument [Member] | Coal Contract [Member] | Coal sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	3,449	3,132	4,806	2,308
Designated as Hedging Instrument [Member] | Coal Contract [Member] | Coal purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	(2,041)	(942)	(2,162)	(511)
Sales Revenue, Net [Member] | Designated as Hedging Instrument [Member] | Coal Contract [Member] | Coal sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion	1,639	911	2,568	2,822
Cost of Sales [Member] | Designated as Hedging Instrument [Member] | Coal Contract [Member] | Coal purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion	(747)	123	(1,222)	(633)
Change in Fair Value of Coal Derivatives and Coal Trading Activity, Net [Member] | Not Designated as Hedging Instrument [Member] | Coal Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	1,610	(10,668)	455	(5,089)
Change in Fair Value of Coal Derivatives and Coal Trading Activity, Net [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	238	0	(21)	0
Other Operating Income (Expense) [Member] | Not Designated as Hedging Instrument [Member] | Coal Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gain (Loss) on Derivatives	502	9,929	4,699	25,725
Other Operating Income (Expense) [Member] | Not Designated as Hedging Instrument [Member] | Heating Oil-Diesel Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Heating oil realized and unrealized gains and losses	(3,746)	(288)	(6,709)	(9,760)
Other Operating Income (Expense) [Member] | Not Designated as Hedging Instrument [Member] | Heating Oil-Fuel Surcharges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Heating oil realized and unrealized gains and losses	$ (104)	$ (222)	$ (405)	$ (817)