Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Major Customers) (Details)

v2.4.0.6
Summary of Significant Accounting Policies (Major Customers) (Details) (Sales Revenue, Goods, Net [Member], Customer Concentration Risk [Member])
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Concentration Risk [Line Items]      
Concentration Risk, Percentage 100.00% 100.00% 100.00%
Shell Trading Company [Member]
     
Concentration Risk [Line Items]      
Concentration Risk, Percentage 39.00% 45.00% 44.00%
Plains Marketing, L.P. [Member]
     
Concentration Risk [Line Items]      
Concentration Risk, Percentage 15.00% 17.00% 20.00%
Enterprise Crude Oil, LLC [Member]
     
Concentration Risk [Line Items]      
Concentration Risk, Percentage 32.00% 16.00% 0.00%
Louis Dreyfus Energy Services [Member]
     
Concentration Risk [Line Items]      
Concentration Risk, Percentage 2.00% 4.00% 13.00%
Other [Member]
     
Concentration Risk [Line Items]      
Concentration Risk, Percentage 12.00% 18.00% 23.00%