Annual report pursuant to Section 13 and 15(d)

Revenue (Revenues from Contracts with Customers) (Details)

v3.20.1
Revenue (Revenues from Contracts with Customers) (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disaggregation of Revenue [Line Items]                      
Royalties                 $ (12,251) $ (15,076) $ (11,558)
Total revenue, net $ 21,923 $ 17,603 $ 25,230 $ 19,765 $ 27,606 $ 25,266 $ 24,426 $ 27,645 84,521 104,943 77,025
Sales Under COSPA [Member]                      
Disaggregation of Revenue [Line Items]                      
Revenue from customer contracts                 86,554 104,891 74,693
Gabonese Government Share Of Profit Oil [Member]                      
Disaggregation of Revenue [Line Items]                      
Revenue from customer contracts                   2,193 11,638
Revenue not from customer contracts                 7,268 9,385  
US Crude Oil And Natural Gas [Member]                      
Disaggregation of Revenue [Line Items]                      
Revenue from customer contracts                   5 47
Carried Interest Recoupment [Member]                      
Disaggregation of Revenue [Line Items]                      
Carried interest recoupment                 $ 2,950 $ 3,545 $ 2,205