Derivative Instruments And Hedging Activities (Volumes Under Derivative Contracts Related To Oil And Gas Producing Activities) (Details)	3 Months Ended
	Mar. 31, 2012 bbl
Minimum [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Weighted Average Price	95.83
Current Remaining Year [Member] | Crude Oil [Member] | Collar [Member]
Average Monthly Volumes	75,000
Current Remaining Year [Member] | Crude Oil [Member] | Brent [Member] | Swap [Member]
Average Monthly Volumes	11,400
Weighted Average Price	103.20
Current Remaining Year [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Average Monthly Volumes	118,600
Current Remaining Year [Member] | Natural Gas [Member] | Swap [Member]
Average Monthly Volumes	771,100,000
Weighted Average Price	4.32
Current Remaining Year [Member] | Natural Gas [Member] | Collar [Member]
Average Monthly Volumes	162,200,000
Current Remaining Year [Member] | Maximum [Member] | Crude Oil [Member] | Collar [Member]
Weighted Average Price	118.57
Current Remaining Year [Member] | Maximum [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Weighted Average Price	118.06
Current Remaining Year [Member] | Maximum [Member] | Natural Gas [Member] | Collar [Member]
Weighted Average Price	5.09
Current Remaining Year [Member] | Minimum [Member] | Crude Oil [Member] | Collar [Member]
Weighted Average Price	96.67
Current Remaining Year [Member] | Minimum [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Weighted Average Price	99.52
Current Remaining Year [Member] | Minimum [Member] | Natural Gas [Member] | Collar [Member]
Weighted Average Price	4.75
Next Year [Member] | Crude Oil [Member] | Brent [Member] | Swap [Member]
Average Monthly Volumes	41,700
Weighted Average Price	99.15
Next Year [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Average Monthly Volumes	50,000
Next Year [Member] | Natural Gas [Member] | Swap [Member]
Average Monthly Volumes	500,000,000
Weighted Average Price	4.09
Next Year [Member] | Maximum [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Weighted Average Price	105.50