Derivative Activities (Fair Value Of Derivative Contracts) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Current asset derivatives	$ 61,281	$ 32,683
Noncurrent asset derivatives	115,797	70,570
Asset derivatives, Total	177,078	103,253
Asset derivative instruments	177,078	103,253
Current liability derivatives	9,473	9,569
Noncurrent liability derivatives	20,391	16,906
Liability derivatives, Total	29,864	26,475
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Current asset derivatives	61,281	32,683
Noncurrent asset derivatives	115,797	70,550
Asset derivatives, Total	177,078	103,233
Asset derivative instruments	177,078	103,233
Current liability derivatives	630	1,284
Noncurrent liability derivatives	2,992	1,218
Liability derivatives, Total	3,622	2,502
Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Noncurrent asset derivatives		20
Asset derivatives, Total		20
Asset derivative instruments		20
Current liability derivatives	8,843	8,285
Noncurrent liability derivatives	17,399	15,688
Liability derivatives, Total	$ 26,242	$ 23,973