Financial Instruments (Details)	Jun. 30, 2011 MMBtud	Dec. 31, 2010 MMBtud
2011 [Member] | Natural gas [Member] | Calls [Member]
Derivative [Line Items]
Notional volumes of commodity positions	10,000	10,000
2011 [Member] | Natural gas [Member] | Call Spreads [Member]
Derivative [Line Items]
Notional volumes of commodity positions	7,100	7,100
2011 [Member] | Natural gas [Member] | Swaps [Member]
Derivative [Line Items]
Notional volumes of commodity positions	10,000	10,000
2011 [Member] | NGL [Member] | Swaps [Member]
Derivative [Line Items]
Notional volumes of commodity positions	1,500	1,500
2011 [Member] | NGL [Member] | Puts [Member]
Derivative [Line Items]
Notional volumes of commodity positions	7,950	7,950
2011 [Member] | Crude oil [Member] | Puts [Member]
Derivative [Line Items]
Notional volumes of commodity positions	2,700	2,700
2012 [Member] | Natural gas [Member] | Calls [Member]
Derivative [Line Items]
Notional volumes of commodity positions	0	0
2012 [Member] | Natural gas [Member] | Call Spreads [Member]
Derivative [Line Items]
Notional volumes of commodity positions	0	0
2012 [Member] | Natural gas [Member] | Swaps [Member]
Derivative [Line Items]
Notional volumes of commodity positions	0	0
2012 [Member] | NGL [Member] | Swaps [Member]
Derivative [Line Items]
Notional volumes of commodity positions	0	0
2012 [Member] | NGL [Member] | Puts [Member]
Derivative [Line Items]
Notional volumes of commodity positions	4,500	3,500
2012 [Member] | Crude oil [Member] | Puts [Member]
Derivative [Line Items]
Notional volumes of commodity positions	1,500	1,500
2013 [Member] | Natural gas [Member] | Calls [Member]
Derivative [Line Items]
Notional volumes of commodity positions	0	0
2013 [Member] | Natural gas [Member] | Call Spreads [Member]
Derivative [Line Items]
Notional volumes of commodity positions	0	0
2013 [Member] | Natural gas [Member] | Swaps [Member]
Derivative [Line Items]
Notional volumes of commodity positions	0	0
2013 [Member] | NGL [Member] | Swaps [Member]
Derivative [Line Items]
Notional volumes of commodity positions	0	0
2013 [Member] | NGL [Member] | Puts [Member]
Derivative [Line Items]
Notional volumes of commodity positions	1,300	0
2013 [Member] | Crude oil [Member] | Puts [Member]
Derivative [Line Items]
Notional volumes of commodity positions	750	400