Derivatives (Fair Value Of Derivative Instruments And Locations In Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Current derivative asset	$ 42,846	$ 31,938
Non-current derivative asset	9,507	4,514
Total derivatives designated as hedging instruments, assets	52,353	36,452
Total derivatives assets	52,353	36,452
Current portion of derivative liabilities	0	2,657
Non-current derivative liabilities	635	0
Total derivatives designated as hedging instruments, liabilities	635	2,657
Total derivative liabilities	635	2,657
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Current derivative asset	42,846	31,938
Non-current derivative asset	9,507	4,514
Current portion of derivative liabilities	0	2,657
Non-current derivative liabilities	$ 635	$ 0