Summary of Significant Accounting Policies (Major Customers) (Details) (Sales Revenue, Goods, Net [Member], Customer Concentration Risk [Member])
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12 Months Ended | ||
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Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2010
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Concentration Risk [Line Items] | |||
Concentration Risk, Percentage | 100.00% | 100.00% | 100.00% |
Shell Trading Company [Member]
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Concentration Risk [Line Items] | |||
Concentration Risk, Percentage | 39.00% | 45.00% | 44.00% |
Plains Marketing, L.P. [Member]
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Concentration Risk [Line Items] | |||
Concentration Risk, Percentage | 15.00% | 17.00% | 20.00% |
Enterprise Crude Oil, LLC [Member]
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Concentration Risk [Line Items] | |||
Concentration Risk, Percentage | 32.00% | 16.00% | 0.00% |
Louis Dreyfus Energy Services [Member]
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Concentration Risk [Line Items] | |||
Concentration Risk, Percentage | 2.00% | 4.00% | 13.00% |
Other [Member]
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Concentration Risk [Line Items] | |||
Concentration Risk, Percentage | 12.00% | 18.00% | 23.00% |