Derivatives (Disclosure Of Fair Value Of Derivatives) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Derivative Asset	$ 15,151	$ 19,954
Derivative Liability	0	(12)
Derivative Assets	84,763	67,681
Derivative Liabilities	(69,612)	(47,739)
Net derivatives as classified in the balance sheet	15,151	19,942
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Assets	83,662	66,772
Derivative Liabilities	(69,397)	(47,713)
Not Designated as Hedging Instrument [Member] | Coal Contract [Member]
Derivative [Line Items]
Derivative Assets	75,886	55,327
Derivative Liabilities	(67,944)	(45,763)
Netting [Member]
Derivative [Line Items]
Derivative Asset	(69,612)	(47,727)
Derivative Liability	69,612	47,727
Heating Oil-Diesel Purchases [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Price Risk Derivative Instruments Not Designated as Hedging Instruments Asset, at Fair Value	2,683	4,681
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value
Heating Oil-Fuel Surcharges [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Price Risk Derivative Instruments Not Designated as Hedging Instruments Asset, at Fair Value	152	422
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value
Coal Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Assets	1,101	909
Derivative Liabilities	(215)	(26)
Coal Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Price Risk Derivative Instruments Not Designated as Hedging Instruments Asset, at Fair Value	4,543	6,342
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value	(1,453)	(1,950)
Natural Gas [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Price Risk Derivative Instruments Not Designated as Hedging Instruments Asset, at Fair Value	398	0
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value	$ 0	$ 0