Derivatives (Fair Value Of Derivative Instruments And Locations In Balance Sheets) (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Current derivative assets	$ 5,402	$ 5,568
Non-current derivative assets	3,028	2,537
Total derivatives assets	8,430	8,105
Current portion of derivative liabilities	10,314	14,446
Long-term derivative liabilities	1,718	4,359
Total derivative liabilities	12,032	18,805
Interest Rate Swaps [Member] | Designated As Hedging Instrument [Member]
Current portion of derivative liabilities	0	1,139
Long-term derivative liabilities	0	475
Designated As Hedging Instrument [Member]
Total derivatives assets	8,430	7,628
Total derivative liabilities	11,693	18,664
Designated As Hedging Instrument [Member] | Commodity Contract [Member]
Current derivative assets	5,402	5,091
Non-current derivative assets	3,028	2,537
Current portion of derivative liabilities	9,975	13,166
Long-term derivative liabilities	1,718	3,884
Not Designated As Hedging Instrument [Member]
Total derivatives assets	0	477
Total derivative liabilities	339	141
Not Designated As Hedging Instrument [Member] | Commodity Contract [Member]
Current derivative assets	0	477
Not Designated As Hedging Instrument [Member] | Commodity Basis Swap [Member]
Current portion of derivative liabilities	$ 339	$ 141