Financial Instruments (Details 3) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Interest Rate Swaps [Member] | Interest and other financing costs [Member] | Cash Flow Hedging [Member]
Derivatives in ASC 815 Cash Flow Hedging Relationships
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ (83)	$ (121)	$ (180)	$ (254)
Interest Rate Swaps [Member] | Interest and other financing costs [Member] | Not designated [Member]
Derivatives Not Designated as Hedging Instruments Under ASC 820
Amount of Gain (Loss) Recognized in Income on Derivative	(381)	(512)	(563)	(1,978)
Natural Gas [Member] | Natural gas sales [Member] | Cash Flow Hedging [Member]
Derivatives in ASC 815 Cash Flow Hedging Relationships
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(1,470)	(1,472)	(2,924)	(2,912)
Natural Gas [Member] | Natural gas sales [Member] | Not designated [Member]
Derivatives Not Designated as Hedging Instruments Under ASC 820
Amount of Gain (Loss) Recognized in Income on Derivative	(65)	116	(128)	(108)
Natural Gas [Member] | Cash Flow Hedging [Member]
Derivatives in ASC 815 Cash Flow Hedging Relationships
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	(26)	(70)	(83)	(2,083)
Natural Gas Liquids [Member] | Natural gas liquids sales [Member] | Cash Flow Hedging [Member]
Derivatives in ASC 815 Cash Flow Hedging Relationships
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(6,816)	253	(12,088)	(1,401)
Amount of Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	(177)	27	(317)	(29)
Natural Gas Liquids [Member] | Natural gas liquids sales [Member] | Not designated [Member]
Derivatives Not Designated as Hedging Instruments Under ASC 820
Amount of Gain (Loss) Recognized in Income on Derivative	(281)	146	(84)	151
Natural Gas Liquids [Member] | Cash Flow Hedging [Member]
Derivatives in ASC 815 Cash Flow Hedging Relationships
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	(463)	14,926	(12,599)	19,855
Crude Oil [Member] | Condensate and other [Member] | Cash Flow Hedging [Member]
Derivatives in ASC 815 Cash Flow Hedging Relationships
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(1,573)	1,864	(3,132)	4,235
Amount of Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	(93)	82	40	107
Crude Oil [Member] | Condensate and other [Member] | Not designated [Member]
Derivatives Not Designated as Hedging Instruments Under ASC 820
Amount of Gain (Loss) Recognized in Income on Derivative	396	334	749	83
Crude Oil [Member] | Cash Flow Hedging [Member]
Derivatives in ASC 815 Cash Flow Hedging Relationships
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	482	5,252	(2,975)	2,901
Cash Flow Hedging [Member]
Derivatives in ASC 815 Cash Flow Hedging Relationships
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	(7)	20,108	(15,657)	20,673
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(9,942)	524	(18,324)	(332)
Amount of Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	(270)	109	(277)	78
Not designated [Member]
Derivatives Not Designated as Hedging Instruments Under ASC 820
Amount of Gain (Loss) Recognized in Income on Derivative	$ (331)	$ 84	$ (26)	$ (1,852)