Impact of Derivative Instruments on Statement of Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Commodity Price Risk Management (loss), net
Derivative [Line Items]
Net settlements	$ (4,459)	$ (2,051)	$ (21,511)	$ 9,629
Net change in fair value of unsettled derivatives	94,672	(22,087)	34,172	(31,704)
Total commodity price risk management gain (loss), net	90,213	(24,138)	12,661	(22,075)
Sales From Natural Gas Marketing
Derivative [Line Items]
Net settlements	210	240	(376)	267
Net change in fair value of unsettled derivatives	170	(311)	123	340
Total commodity price risk management gain (loss), net	380	(71)	(253)	607
Cost of Natural Gas Marketing
Derivative [Line Items]
Net settlements	(182)	(188)	502	(125)
Net change in fair value of unsettled derivatives	(191)	278	(199)	(281)
Total commodity price risk management gain (loss), net	$ (373)	$ 90	$ 303	$ (406)