Derivative Instruments (Schedule Of U.S. Crude Oil Derivative Positions) (Details) (U.S. Crude Oil Derivative Positions [Member])	Jun. 30, 2012 bbls
2012 [Member]
Derivative [Line Items]
Volume (in Bbls)	883,200
Weighted Average Floor Price ($/Bbls)	86.15
Weighted Average Ceiling Price ($/Bbls)	105.91
2013 [Member]
Derivative [Line Items]
Volume (in Bbls)	1,861,500
Weighted Average Floor Price ($/Bbls)	87.57
Weighted Average Ceiling Price ($/Bbls)	104.82
2014 [Member]
Derivative [Line Items]
Volume (in Bbls)	1,095,000
Weighted Average Floor Price ($/Bbls)	91.75
Weighted Average Ceiling Price ($/Bbls)	103.88
2015 [Member]
Derivative [Line Items]
Volume (in Bbls)	620,500
Weighted Average Floor Price ($/Bbls)	92.79
Weighted Average Ceiling Price ($/Bbls)	97.18