Derivative Instruments Derivative Instruments (Schedule Of U.S. Crude Oil Protective Put Spreads) (Details) (Protective Put Spreads [Member])	Dec. 31, 2012 bbls
2014 [Member]
Derivative [Line Items]
Volumes (in Bbls)	182,500
Weighted Average Short Put Price ($/Bbl)	65.00
Weighted Average Put Spread ($/Bbl)	20.00
2015 [Member]
Derivative [Line Items]
Volumes (in Bbls)	365,000
Weighted Average Short Put Price ($/Bbl)	65.00
Weighted Average Put Spread ($/Bbl)	20.00
2016 [Member]
Derivative [Line Items]
Volumes (in Bbls)	244,000
Weighted Average Short Put Price ($/Bbl)	65.00
Weighted Average Put Spread ($/Bbl)	20.00