Impact of Derivative Instruments on Statement of Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Commodity Price Risk Management, net [Member]
Derivative [Line Items]
Realized Gains (Losses)	$ 16,179	$ 1,803	$ 26,106	$ 5,591
Unrealized Gains (Losses)	22,550	18,734	24,124	(8,936)
Total Derivative Gain (Loss)	38,729	20,537	50,230	(3,345)
Sales From Natural Gas Marketing [Member]
Derivative [Line Items]
Realized Gains (Losses)	752	492	1,545	1,634
Unrealized Gains (Losses)	(1,071)	(17)	(996)	(1,034)
Total Derivative Gain (Loss)	(319)	475	549	600
Cost of Natural Gas Marketing [Member]
Derivative [Line Items]
Realized Gains (Losses)	(718)	(401)	(1,463)	(1,361)
Unrealized Gains (Losses)	1,067	(66)	951	876
Total Derivative Gain (Loss)	349	(467)	(512)	(485)
Reclassification of Realized Gains (Losses) Included in Prior Periods Unrealized [Member] | Commodity Price Risk Management, net [Member]
Derivative [Line Items]
Realized Gains (Losses)	13,503	763	16,046	6,612
Unrealized Gains (Losses)	(13,503)	(763)	(16,046)	(6,612)
Total Derivative Gain (Loss)	0	0	0	0
Reclassification of Realized Gains (Losses) Included in Prior Periods Unrealized [Member] | Sales From Natural Gas Marketing [Member]
Derivative [Line Items]
Realized Gains (Losses)	749	473	1,110	1,373
Unrealized Gains (Losses)	(749)	(473)	(1,110)	(1,373)
Total Derivative Gain (Loss)	0	0	0	0
Reclassification of Realized Gains (Losses) Included in Prior Periods Unrealized [Member] | Cost of Natural Gas Marketing [Member]
Derivative [Line Items]
Realized Gains (Losses)	(692)	(370)	(970)	(1,076)
Unrealized Gains (Losses)	692	370	970	1,076
Total Derivative Gain (Loss)	0	0	0	0
Realized and Unrealized Gains (Losses) for the Current Period [Member] | Commodity Price Risk Management, net [Member]
Derivative [Line Items]
Realized Gains (Losses)	2,676	1,040	10,060	(1,021)
Unrealized Gains (Losses)	36,053	19,497	40,170	(2,324)
Total Derivative Gain (Loss)	38,729	20,537	50,230	(3,345)
Realized and Unrealized Gains (Losses) for the Current Period [Member] | Sales From Natural Gas Marketing [Member]
Derivative [Line Items]
Realized Gains (Losses)	3	19	435	261
Unrealized Gains (Losses)	(322)	456	114	339
Total Derivative Gain (Loss)	(319)	475	549	600
Realized and Unrealized Gains (Losses) for the Current Period [Member] | Cost of Natural Gas Marketing [Member]
Derivative [Line Items]
Realized Gains (Losses)	(26)	(31)	(493)	(285)
Unrealized Gains (Losses)	375	(436)	(19)	(200)
Total Derivative Gain (Loss)	$ 349	$ (467)	$ (512)	$ (485)