Derivatives (Disclosure Of Fair Value Of Derivatives) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	$ (89,918)	$ (98,686)
Derivative Liability, Fair Value, Gross Asset	89,918	98,686
Derivative Asset	18,802	13,557
Derivative Liability	(831)	(766)
Net derivatives as classified in the balance sheet	17,971	12,791
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Price Risk Derivative Instruments Not Designated as Hedging Instruments Asset, at Fair Value	104,118	105,708
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value	(90,617)	(96,960)
Not Designated as Hedging Instrument [Member] | Coal Contract [Member]
Derivative [Line Items]
Derivative Assets	85,130	96,898
Derivative Liabilities	(82,582)	(93,272)
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	5,444	300
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value	0	0
Coal Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Assets	4,602	6,535
Derivative Liabilities	(132)	(2,492)
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	12,551	8,510
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value	(8,035)	(3,688)
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	993	0
Price Risk Derivative Instruments Not Designated as Hedging Instruments Liability, at Fair Value	0	0
Price Risk Derivative [Member]
Derivative [Line Items]
Derivative Assets	108,720	112,243
Derivative Liabilities	$ (90,749)	$ (99,452)