Derivative Instruments (Schedule Of U.S. Crude Oil Derivative Positions) (Details) (U.S. Crude Oil Derivative Positions [Member])	Mar. 31, 2013 bbls
2013 [Member]
Derivative [Line Items]
Volumes (in Bbls)	2,227,500
Weighted Average Floor Price ($/Bbls)	89.24
Weighted Average Ceiling Price ($/Bbls)	101.93
2014 [Member]
Derivative [Line Items]
Volumes (in Bbls)	2,737,500
Weighted Average Floor Price ($/Bbls)	90.27
Weighted Average Ceiling Price ($/Bbls)	98.15
2015 [Member]
Derivative [Line Items]
Volumes (in Bbls)	1,624,250
Weighted Average Floor Price ($/Bbls)	89.58
Weighted Average Ceiling Price ($/Bbls)	95.75
2016 [Member]
Derivative [Line Items]
Volumes (in Bbls)	244,000
Weighted Average Floor Price ($/Bbls)	85.00
Weighted Average Ceiling Price ($/Bbls)	104.00