Financial Instruments (Details 1) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Fair value of derivative asset
Total	$ 29,229	$ 19,779
Fair value of derivative liability
Total	7,461	11,826
Total designated assets	22,784	14,879
Total not designated (liabilities)/assets	(1,016)	(6,926)
Natural Gas [Member] | Level 1 [Member] | Short-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0	0
Natural Gas [Member] | Level 1 [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0
Fair value of derivative liability
Total	0	0
Natural Gas [Member] | Level 1 [Member] | Long-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0
Natural Gas [Member] | Level 1 [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0
Natural Gas Liquids [Member] | Level 1 [Member] | Short-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0	0
Fair value of derivative liability
Total	0	0
Natural Gas Liquids [Member] | Level 1 [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0	0
Natural Gas Liquids [Member] | Level 1 [Member] | Long-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0	0
Fair value of derivative liability
Total	0
Natural Gas Liquids [Member] | Level 1 [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0
Crude Oil [Member] | Level 1 [Member] | Short-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0	0
Crude Oil [Member] | Level 1 [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0	0
Crude Oil [Member] | Level 1 [Member] | Long-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0	0
Crude Oil [Member] | Level 1 [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0
Level 1 [Member]
Fair value of derivative asset
Total	0	0
Fair value of derivative liability
Total	0	0
Total designated assets	0	0
Total not designated (liabilities)/assets	0	0
Level 1 [Member] | Interest Rate [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative liability
Total	0	0
Level 1 [Member] | Interest Rate [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative liability
Total	0	0
Natural Gas [Member] | Level 2 [Member] | Short-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0	0
Natural Gas [Member] | Level 2 [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0
Fair value of derivative liability
Total	129	82
Natural Gas [Member] | Level 2 [Member] | Long-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0
Natural Gas [Member] | Level 2 [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0
Natural Gas Liquids [Member] | Level 2 [Member] | Short-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0	0
Fair value of derivative liability
Total	0	0
Natural Gas Liquids [Member] | Level 2 [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0	0
Natural Gas Liquids [Member] | Level 2 [Member] | Long-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0	0
Fair value of derivative liability
Total	0
Natural Gas Liquids [Member] | Level 2 [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0
Crude Oil [Member] | Level 2 [Member] | Short-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0	0
Crude Oil [Member] | Level 2 [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0	0
Crude Oil [Member] | Level 2 [Member] | Long-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0	0
Crude Oil [Member] | Level 2 [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0
Level 2 [Member]
Fair value of derivative asset
Total	0	0
Fair value of derivative liability
Total	4,731	6,959
Total designated assets	0	0
Total not designated (liabilities)/assets	(4,731)	(6,959)
Level 2 [Member] | Interest Rate [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative liability
Total	4,426	4,408
Level 2 [Member] | Interest Rate [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative liability
Total	176	2,469
Natural Gas [Member] | Level 3 [Member] | Short-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0	87
Natural Gas [Member] | Level 3 [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0
Fair value of derivative liability
Total	0	0
Natural Gas [Member] | Level 3 [Member] | Long-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0
Natural Gas [Member] | Level 3 [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0
Natural Gas Liquids [Member] | Level 3 [Member] | Short-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	5,076	6,812
Fair value of derivative liability
Total	2,730	4,867
Natural Gas Liquids [Member] | Level 3 [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	1,285	14
Natural Gas Liquids [Member] | Level 3 [Member] | Long-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	8,947	6,391
Fair value of derivative liability
Total	0
Natural Gas Liquids [Member] | Level 3 [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	611
Crude Oil [Member] | Level 3 [Member] | Short-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	4,417	904
Crude Oil [Member] | Level 3 [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	1,323	19
Crude Oil [Member] | Level 3 [Member] | Long-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	7,074	5,552
Crude Oil [Member] | Level 3 [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	496
Level 3 [Member]
Fair value of derivative asset
Total	29,229	19,779
Fair value of derivative liability
Total	2,730	4,867
Total designated assets	22,784	14,879
Total not designated (liabilities)/assets	3,715	33
Level 3 [Member] | Interest Rate [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative liability
Total	0	0
Level 3 [Member] | Interest Rate [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative liability
Total	0	0
Natural Gas [Member] | Short-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0	87
Natural Gas [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0
Fair value of derivative liability
Total	129	82
Natural Gas [Member] | Long-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	0
Natural Gas [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	0
Natural Gas Liquids [Member] | Short-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	5,076	6,812
Fair value of derivative liability
Total	2,730	4,867
Natural Gas Liquids [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	1,285	14
Natural Gas Liquids [Member] | Long-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	8,947	6,391
Fair value of derivative liability
Total	0
Natural Gas Liquids [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	611
Crude Oil [Member] | Short-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	4,417	904
Crude Oil [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	1,323	19
Crude Oil [Member] | Long-term [Member] | Designated as Hedging Instrument [Member]
Fair value of derivative asset
Total	7,074	5,552
Crude Oil [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative asset
Total	496
Interest Rate [Member] | Short-term [Member] | Not designated [Member]
Fair value of derivative liability
Total	4,426	4,408
Interest Rate [Member] | Long-term [Member] | Not designated [Member]
Fair value of derivative liability
Total	$ 176	$ 2,469