Derivative Activities (Fair Value Of Derivative Contracts) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Current asset derivatives	$ 42,482	$ 32,683
Noncurrent asset derivatives	81,450	70,570
Asset derivative instruments	123,932	103,253
Asset derivative instruments	123,932	103,253
Current liability derivatives	5,176	9,569
Noncurrent liability derivatives	14,156	16,906
Liability derivative instruments	19,332	26,475
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Current asset derivatives	42,482	32,683
Noncurrent asset derivatives	81,450	70,550
Asset derivative instruments	123,932	103,233
Asset derivative instruments	123,932	103,233
Current liability derivatives	565	1,284
Noncurrent liability derivatives	5,497	1,218
Liability derivative instruments	6,062	2,502
Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Noncurrent asset derivatives		20
Asset derivative instruments		20
Asset derivative instruments		20
Current liability derivatives	4,611	8,285
Noncurrent liability derivatives	8,659	15,688
Liability derivative instruments	$ 13,270	$ 23,973