Derivative Instruments (Schedule Of U.S. Crude Oil Derivative Positions) (Details) (U.S. Crude Oil Derivative Positions [Member])	Dec. 31, 2012 bbls
2013 [Member]
Derivative [Line Items]
Volumes (in Bbls)	2,774,000
Weighted Average Floor Price ($/Bbls)	88.91
Weighted Average Ceiling Price ($/Bbls)	102.43
2014 [Member]
Derivative [Line Items]
Volumes (in Bbls)	2,555,000
Weighted Average Floor Price ($/Bbls)	90.06
Weighted Average Ceiling Price ($/Bbls)	98.51
2015 [Member]
Derivative [Line Items]
Volumes (in Bbls)	1,441,750
Weighted Average Floor Price ($/Bbls)	89.54
Weighted Average Ceiling Price ($/Bbls)	96.49
2016 [Member]
Derivative [Line Items]
Volumes (in Bbls)	244,000
Weighted Average Floor Price ($/Bbls)	85.00
Weighted Average Ceiling Price ($/Bbls)	104.00