Derivative Instruments and Hedging Activities (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Apr. 01, 2014
Effect of derivative instruments on the Consolidated Statement of Operations
Gain (loss) related to amounts previously frozen in accumulated OCI, reclassified into income				$ (73,400,000)
Derivatives Designated as Hedges
Effect of derivative instruments on the Consolidated Statement of Operations
Amount of gain (loss) reclassified from accumulated OCI into income (effective portion)	(144,203,000)	57,002,000	236,326,000
Derivatives Designated as Hedges | Natural gas
Effect of derivative instruments on the Consolidated Statement of Operations
Amount of gain (loss) reclassified from accumulated OCI into income (effective portion)	(143,577,000)	52,733,000	225,108,000
Derivatives Designated as Hedges | Crude oil and condensate
Effect of derivative instruments on the Consolidated Statement of Operations
Amount of gain (loss) reclassified from accumulated OCI into income (effective portion)	(626,000)	4,269,000	11,218,000
Derivatives Designated as Hedges | Commodity contracts
Effect of derivative instruments on the Consolidated Statement of Operations
Amount of gain (loss) recognized in OCI on derivatives (effective portion)	$ (133,310,000)	$ (4,523,000)	$ 88,705,000