Derivative Activities (Fair Value Of Derivative Contracts) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Current asset derivatives	$ 40,809	$ 45,522
Noncurrent asset derivatives	90,499	76,621
Asset derivative instruments	131,308	122,143
Current liability derivatives	8,248	8,727
Noncurrent liability derivatives	6,829	16,993
Liability derivative instruments	15,077	25,720
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Current asset derivatives	40,809	45,522
Noncurrent asset derivatives	90,499	76,621
Asset derivative instruments	131,308	122,143
Current liability derivatives	3,724	4,130
Noncurrent liability derivatives	2,152	9,354
Liability derivative instruments	5,876	13,484
Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Current liability derivatives	4,524	4,597
Noncurrent liability derivatives	4,677	7,639
Liability derivative instruments	$ 9,201	$ 12,236