Derivative Instruments and Hedging Activities (Details 4) (USD $)	3 Months Ended			6 Months Ended		9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2014		Sep. 30, 2013
Derivative instruments and hedging activities
Ineffectiveness related to derivative instruments	$ 0		$ 0			$ 0		$ 0
Amount of gain (loss) reclassified from accumulated other comprehensive income (loss) into income (effective portion)	(21,557,000)	[1]	19,684,000	(44,514,000)	[1]	(115,288,000)	[1]	36,876,000
Unrealized Gain (Loss) on Derivatives						44,766,000		0
Gain (loss) on derivative instruments	50,349,000		0			25,064,000		0
Total	50,349,000		19,684,000			(45,711,000)		36,876,000
Natural Gas Revenues
Derivative instruments and hedging activities
Amount of gain (loss) reclassified from accumulated other comprehensive income (loss) into income (effective portion)	(21,427,000)	[1]	20,766,000			(114,304,000)	[1]	33,822,000
Crude Oil and Condensate Revenues
Derivative instruments and hedging activities
Amount of gain (loss) reclassified from accumulated other comprehensive income (loss) into income (effective portion)	(130,000)	[1]	(1,082,000)			(984,000)	[1]	3,054,000
Commodity contracts
Derivative instruments and hedging activities
Amount of gain (loss) recognized in other comprehensive income (loss) on derivative (effective portion)	0		(2,384,000)			(133,310,000)		51,783,000
Derivatives Designated as Hedges
Derivative instruments and hedging activities
Realized gain (loss) on derivative instruments	0		19,684,000			(70,775,000)		36,876,000
Derivatives Designated as Hedges | Natural Gas Revenues
Derivative instruments and hedging activities
Realized gain (loss) on derivative instruments	0		20,766,000			(70,557,000)		33,822,000
Derivatives Designated as Hedges | Crude Oil and Condensate Revenues
Derivative instruments and hedging activities
Realized gain (loss) on derivative instruments	0		(1,082,000)			(218,000)		3,054,000
Derivatives Not Designated as Hedges
Derivative instruments and hedging activities
Unrealized Gain (Loss) on Derivatives	31,833,000		0			44,766,000		0
Derivatives Not Designated as Hedges | Natural Gas Revenues
Derivative instruments and hedging activities
Realized gain (loss) on derivative instruments	(21,427,000)		0			(43,747,000)		0
Derivatives Not Designated as Hedges | Crude Oil and Condensate Revenues
Derivative instruments and hedging activities
Realized gain (loss) on derivative instruments	(130,000)		0			(766,000)		0
Derivatives Not Designated as Hedges | Gain (loss) on derivative instruments
Derivative instruments and hedging activities
Realized gain (loss) on derivative instruments	$ 40,073,000		$ 0			$ 24,811,000		$ 0

[1] The Company ceased hedge accounting effective April 1, 2014. For the three and nine months ended September 30, 2014, a loss of approximately $21.6 million and $44.5 million, respectively, were reclassified into income. These amounts were previously frozen in accumulated other comprehensive income (loss).