Derivative Instruments (Schedule Of Derivative Assets And Liabilities Statement) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Derivative long-term assets	$ 3,696	$ 23
Derivative assets	8,200	2,673
Derivative long-term liabilities	36,633	61,127
Derivative liabilities	49,068	74,299
Derivatives Designated as Cash Flow Hedges [Member]
Derivative assets	8,200	2,673
Derivative liabilities	11,722	14,692
Derivatives Designated as Cash Flow Hedges [Member] | Commodity Derivatives [Member]
Derivative current assets	4,504	2,650
Derivative long-term assets	3,696	23
Derivative current liabilities	11,357	11,421
Derivative long-term liabilities	365	3,271
Derivatives Not Designated as Cash Flow Hedges [Member]
Derivative assets	0	0
Derivative liabilities	37,346	59,607
Derivatives Not Designated as Cash Flow Hedges [Member] | Interest Rate [Member]
Derivative current assets	0	0
Derivative long-term assets	0	0
Derivative current liabilities	1,078	1,751
Derivative long-term liabilities	0	833
Derivatives Not Designated as Cash Flow Hedges [Member] | Embedded Derivatives [Member]
Derivative long-term assets	0	0
Derivative long-term liabilities	$ 36,268	$ 57,023