Derivative Instruments and Hedging Activities (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Effect of derivative instruments on the Consolidated Statement of Operations
Ineffectiveness related to derivative instruments	$ 0	$ 0	$ 0
Natural Gas Revenues
Effect of derivative instruments on the Consolidated Statement of Operations
Amount of Gain (Loss) Recognized in Income on Derivative Not Designated		(494)	(965)
Derivatives Designated as Hedging Instruments
Effect of derivative instruments on the Consolidated Statement of Operations
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	57,002	236,326	86,340
Derivatives Designated as Hedging Instruments | Natural Gas Revenues
Effect of derivative instruments on the Consolidated Statement of Operations
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	52,733	225,108	84,937
Derivatives Designated as Hedging Instruments | Crude Oil and Condensate Revenues
Effect of derivative instruments on the Consolidated Statement of Operations
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	4,269	11,218	1,403
Derivatives Designated as Hedging Instruments | Commodity contracts
Effect of derivative instruments on the Consolidated Statement of Operations
Amount of Gain (Loss) Recognized In OCI on Derivative (Effective Portion)	$ (4,523)	$ 88,705	$ 267,667