Summary Of Significant Accounting Policies (Summary Of Volumes Under Derivatives And Forward Sales Contracts) (Details)	12 Months Ended
	Dec. 31, 2011 MBbls
Next Year [Member] | Crude Oil [Member] | Collar [Member]
Derivative [Line Items]
Average Monthly Volumes	75.0
Next Year [Member] | Crude Oil [Member] | Collar 2 [Member]
Derivative [Line Items]
Average Monthly Volumes	139.0
Next Year [Member] | Natural Gas [Member] | Swap [Member]
Derivative [Line Items]
Average Monthly Volumes	750.0
Weighted Average Price	4.35
Next Year [Member] | Natural Gas [Member] | Collar [Member]
Derivative [Line Items]
Average Monthly Volumes	166.7
Next Year [Member] | Brent Crude Oil [Member] | Swap [Member]
Derivative [Line Items]
Average Monthly Volumes	16.0
Weighted Average Price	103.20
Second Year [Member] | Natural Gas [Member] | Swap [Member]
Derivative [Line Items]
Average Monthly Volumes	500.0
Weighted Average Price	4.09
Second Year [Member] | Brent Crude Oil [Member] | Swap [Member]
Derivative [Line Items]
Average Monthly Volumes	41.7
Weighted Average Price	99.15
Second Year [Member] | Brent Crude Oil [Member] | Collar [Member]
Derivative [Line Items]
Average Monthly Volumes	41.7
Maximum [Member] | Next Year [Member] | Crude Oil [Member] | Collar [Member]
Derivative [Line Items]
Weighted Average Price	118.57	[1],[2]
Maximum [Member] | Next Year [Member] | Natural Gas [Member] | Collar [Member]
Derivative [Line Items]
Weighted Average Price	5.09	[1]
Maximum [Member] | Next Year [Member] | Brent Crude Oil [Member] | Collar 2 [Member]
Derivative [Line Items]
Weighted Average Price	117.59	[1]
Maximum [Member] | Second Year [Member] | Brent Crude Oil [Member] | Collar [Member]
Derivative [Line Items]
Weighted Average Price	102.60	[1]
Minimum [Member] | Next Year [Member] | Crude Oil [Member] | Collar [Member]
Derivative [Line Items]
Weighted Average Price	96.67	[1]
Minimum [Member] | Next Year [Member] | Natural Gas [Member] | Collar [Member]
Derivative [Line Items]
Weighted Average Price	4.75	[1]
Minimum [Member] | Next Year [Member] | Brent Crude Oil [Member] | Collar 2 [Member]
Derivative [Line Items]
Weighted Average Price	99.42	[1]
Minimum [Member] | Second Year [Member] | Brent Crude Oil [Member] | Collar [Member]
Derivative [Line Items]
Weighted Average Price	95.00	[1]

[1] The prices quoted in the table above are NYMEX Henry Hub for natural gas. For oil most of the contracts are priced as Brent crude oil.

[2] This contract is priced using NYMEX West Texas Intermediate for crude oil.