Derivative Activities (Fair Value Of Derivative Contracts) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Current asset derivatives	$ 45,522	$ 32,683
Noncurrent asset derivatives	76,621	72,814
Asset derivative instruments	122,143	105,497
Current liability derivatives	8,727	9,569
Noncurrent liability derivatives	16,993	24,489
Liability derivative instruments	25,720	34,058
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Current asset derivatives	45,522	32,683
Noncurrent asset derivatives	76,621	72,794
Asset derivative instruments	122,143	105,477
Current liability derivatives	4,130	1,284
Noncurrent liability derivatives	9,354	8,801
Liability derivative instruments	13,484	10,085
Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Noncurrent asset derivatives		20
Asset derivative instruments		20
Current liability derivatives	4,597	8,285
Noncurrent liability derivatives	7,639	15,688
Liability derivative instruments	$ 12,236	$ 23,973