Annual report pursuant to Section 13 and 15(d)

Segment Information (Segment Activity) (Details)

v3.10.0.1
Segment Information (Segment Activity) (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Segment Reporting Information [Line Items]                      
Revenues-oil and natural gas sales $ 27,606 $ 25,266 $ 24,426 $ 27,645 $ 17,156 $ 18,178 $ 20,425 $ 21,266 $ 104,943 $ 77,025 $ 59,784
Depreciation, depletion and amortization                 5,596 6,457 6,926
Impairment of proved properties                     88
Bad debt expense and other                 (77) 452 1,222
Operating income (loss) $ 15,206 $ 17,320 $ 5,723 $ 13,038 $ 2,495 $ 3,721 $ 5,587 $ 8,148 51,287 19,951 (4,391)
Other, net                 4,332 2,113 (2,015)
Interest expense, net                 (145) (1,414) (2,613)
Income tax expense (benefit)                 (43,254) 10,378 9,248
Additions to oil and natural gas properties and equipment - accrual                 38,634 1,702 (4,061)
Operating Segments | Gabon Segment [Member]                      
Segment Reporting Information [Line Items]                      
Revenues-oil and natural gas sales                 104,938 76,978 59,460
Depreciation, depletion and amortization                 5,176 6,196 6,531
Bad debt expense and other                 (77) 452 1,222
Operating income (loss)                 61,930 28,488 3,901
Other, net                 92 3,142 (22)
Interest expense, net                 (396) (1,414) (2,614)
Income tax expense (benefit)                 (26,670) 11,638 9,248
Additions to oil and natural gas properties and equipment - accrual                 38,430 1,576 (4,242)
Operating Segments | Equatorial Guinea Segment [Member]                      
Segment Reporting Information [Line Items]                      
Operating income (loss)                 (470) (122) (384)
Other, net                 (4) 15 (8)
Additions to oil and natural gas properties and equipment - accrual                 187    
Corporate, Non-Segment                      
Segment Reporting Information [Line Items]                      
Revenues-oil and natural gas sales                 5 47 324
Depreciation, depletion and amortization                 420 261 395
Impairment of proved properties                     88
Operating income (loss)                 (10,173) (8,415) (7,908)
Other, net                 4,244 (1,044) (1,985)
Interest expense, net                 251   1
Income tax expense (benefit)                 (16,584) (1,260)  
Additions to oil and natural gas properties and equipment - accrual                 $ 17 $ 126 $ 181