Derivative Instruments (Schedule Of U.S. Crude Oil Derivative Positions) (Details) (U.S. Crude Oil Derivative Positions [Member])	Mar. 31, 2012
2012 [Member]
Derivative [Line Items]
Volume (in Bbls)	1,320,000
Weighted Average Floor Price ($/Bbls)	86.15
Weighted Average Ceiling Price ($/Bbls)	105.91
2013 [Member]
Derivative [Line Items]
Volume (in Bbls)	1,679,000
Weighted Average Floor Price ($/Bbls)	87.83
Weighted Average Ceiling Price ($/Bbls)	106.94
2014 [Member]
Derivative [Line Items]
Volume (in Bbls)	730,000
Weighted Average Floor Price ($/Bbls)	92.63
Weighted Average Ceiling Price ($/Bbls)	101.33
2015 [Member]
Derivative [Line Items]
Volume (in Bbls)	365,000
Weighted Average Floor Price ($/Bbls)	94.75
Weighted Average Ceiling Price ($/Bbls)	94.75