Annual report pursuant to Section 13 and 15(d)

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

v3.20.4
Summary of Significant Accounting Policies (Major Customers) (Details) - Revenue Benchmark - Customer Concentration Risk
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Shell Trading Company      
Product Information [Line Items]      
Concentration risk, percentage 31.00% 10.00%  
Valero Energy      
Product Information [Line Items]      
Concentration risk, percentage 23.00%    
Rio Energy International, Inc.      
Product Information [Line Items]      
Concentration risk, percentage   26.00% 28.00%
Enterprise Crude Oil, LLC      
Product Information [Line Items]      
Concentration risk, percentage   19.00% 14.00%
Plains Marketing, L.P.      
Product Information [Line Items]      
Concentration risk, percentage   15.00% 21.00%