Derivative Instruments And Hedging Activities (Volumes Under Derivative Contracts Related To Oil And Gas Producing Activities) (Details)	6 Months Ended
	Jun. 30, 2012 bbl
Minimum [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Weighted Average Price	98.44
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	96,600
Weighted Average Price	92.52
Current Remaining Year [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Average Monthly Volumes	99,100
Current Remaining Year [Member] | Natural Gas [Member] | Swap [Member]
Average Monthly Volumes	777,500,000
Weighted Average Price	4.29
Current Remaining Year [Member] | Natural Gas [Member] | Collar [Member]
Average Monthly Volumes	156,700,000
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	118.42
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	99.67
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	88,900
Weighted Average Price	95.28
Next Year [Member] | Crude Oil [Member] | Brent [Member] | Collar [Member]
Average Monthly Volumes	133,300
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	115.85