Derivatives (Net Derivatives As Reflected On The Balance Sheets) (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Derivative assets	$ 41,506	$ 51,068
Net derivatives as reflected on the balance sheet	25,090	23,719
Other Current Assets [Member] | Heating Oil [Member]
Derivative assets	18,101	13,475
Coal [Member]
Coal derivative assets	12,780	15,191
Coal derivative liabilities	$ (5,791)	$ (4,947)