Annual report pursuant to Section 13 and 15(d)

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

v3.6.0.2
Summary of Significant Accounting Policies (Major Customers) (Details) - Sales Revenue, Goods, Net [Member] - Customer Concentration Risk [Member]
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Concentration Risk [Line Items]      
Concentration Risk, Percentage 100.00% 100.00% 100.00%
Enterprise Crude Oil, LLC [Member]      
Concentration Risk [Line Items]      
Concentration Risk, Percentage 43.00% 42.00% 51.00%
Shell Trading Company [Member]      
Concentration Risk [Line Items]      
Concentration Risk, Percentage   9.00% 10.00%
Plains Marketing, L.P. [Member]      
Concentration Risk [Line Items]      
Concentration Risk, Percentage 18.00% 4.00%  
Permian Transport And Trading [Member]      
Concentration Risk [Line Items]      
Concentration Risk, Percentage 16.00% 19.00% 22.00%
Sunoco [Member]      
Concentration Risk [Line Items]      
Concentration Risk, Percentage   15.00% 7.00%
Other [Member]      
Concentration Risk [Line Items]      
Concentration Risk, Percentage 23.00% 11.00% 10.00%