Derivative Instruments And Hedging Activities (Volumes Under Derivative Contracts Related To Oil And Gas Producing Activities) (Details)	9 Months Ended
	Sep. 30, 2011 bbl
Maximum [Member] | Current Remaining Year [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Weighted Average Price	122.80	[1]
Maximum [Member] | Current Remaining Year [Member] | Crude Oil [Member] | Collar [Member]
Weighted Average Price	124.59
Minimum [Member] | Current Remaining Year [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Weighted Average Price	100.00	[1]
Minimum [Member] | Current Remaining Year [Member] | Crude Oil [Member] | Collar [Member]
Weighted Average Price	95.00
Current Remaining Year [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Average Monthly Volumes	50,000
Current Remaining Year [Member] | Crude Oil [Member] | Swap [Member]
Average Monthly Volumes	163,300
Weighted Average Price	82.62
Current Remaining Year [Member] | Crude Oil [Member] | Collar [Member]
Average Monthly Volumes	35,300
Current Remaining Year [Member] | Natural Gas [Member] | Swap [Member]
Average Monthly Volumes	703,300,000
Weighted Average Price	4.93
Maximum [Member] | Next Year [Member] | Crude Oil [Member] | Henry Hub [Member] | Collar 2 [Member]
Weighted Average Price	117.59	[1]
Maximum [Member] | Next Year [Member] | Crude Oil [Member] | Collar [Member]
Weighted Average Price	118.57
Minimum [Member] | Next Year [Member] | Crude Oil [Member] | Henry Hub [Member] | Collar 2 [Member]
Weighted Average Price	99.42	[1]
Minimum [Member] | Next Year [Member] | Crude Oil [Member] | Collar [Member]
Weighted Average Price	96.67
Next Year [Member] | Crude Oil [Member] | Brent [Member] | Swap [Member]
Average Monthly Volumes	16,000
Weighted Average Price	103.20	[1]
Next Year [Member] | Crude Oil [Member] | Brent [Member] | Collar 2 [Member]
Average Monthly Volumes	139,000
Next Year [Member] | Crude Oil [Member] | Collar [Member]
Average Monthly Volumes	75,000
Next Year [Member] | Natural Gas [Member] | Swap [Member]
Average Monthly Volumes	333,300,000
Weighted Average Price	4.70
Next Year [Member] | Natural Gas [Member] | Collar [Member]
Average Monthly Volumes	166,700,000
Maximum [Member] | Second Year [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Weighted Average Price	102.60	[1]
Minimum [Member] | Second Year [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Weighted Average Price	95.00	[1]
Second Year [Member] | Crude Oil [Member] | Brent [Member] | Swap [Member]
Average Monthly Volumes	41,700
Weighted Average Price	99.15	[1]
Second Year [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Average Monthly Volumes	41,700
Maximum [Member] | Natural Gas [Member] | Collar [Member]
Weighted Average Price	5.09
Minimum [Member] | Natural Gas [Member] | Collar [Member]
Weighted Average Price	4.75

[1] The prices quoted in the table above are primarily NYMEX Henry Hub for natural gas and NYMEX West Texas Intermediate for crude oil. As footnoted above these costless collar contracts are priced as Brent crude oil.