Derivatives (Disclosure Of Fair Value Of Derivatives) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	$ (69,032)	$ (47,727)
Derivative Liability, Fair Value, Gross Asset	69,032	47,727
Derivative Asset	17,082	19,954
Derivative Liability	56	12
Net derivatives as classified in the balance sheet	17,026	19,942
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Price Risk Derivative Instruments Not Designated as Hedging Instruments Asset, at Fair Value	84,434	66,772
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value	(69,088)	(47,713)
Not Designated as Hedging Instrument [Member] | Coal Contract [Member]
Derivative [Line Items]
Derivative Assets	75,061	55,327
Derivative Liabilities	(66,137)	(45,763)
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	1,440	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	1	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	1,680	909
Derivative Liabilities	0	(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	7,707	6,342
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value	(2,861)	(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	225	0
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value	(90)	0
Price Risk Derivative [Member]
Derivative [Line Items]
Derivative Assets	86,114	67,681
Derivative Liabilities	$ (69,088)	$ (47,739)