Derivatives (Fair Value Of Derivative Instruments And Locations In Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 31,938	$ 5,568
Non-current derivative assets	4,514	2,537
Total derivatives assets	36,452	8,105
Current portion of derivative liabilities	2,657	14,446
Non-current derivative liabilities	0	4,359
Total derivative liabilities	2,657	18,805
Designated As Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivatives assets	36,452	7,628
Total derivative liabilities	2,657	18,664
Designated As Hedging Instrument [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Current portion of derivative liabilities	0	1,139
Non-current derivative liabilities	0	475
Designated As Hedging Instrument [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	31,938	5,091
Non-current derivative assets	4,514	2,537
Current portion of derivative liabilities	2,657	13,166
Non-current derivative liabilities	0	3,884
Not Designated As Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivatives assets	0	477
Total derivative liabilities	0	141
Not Designated As Hedging Instrument [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	0	477
Not Designated As Hedging Instrument [Member] | Commodity Basis Swap [Member]
Derivatives, Fair Value [Line Items]
Current portion of derivative liabilities	$ 0	$ 141