Annual report pursuant to Section 13 and 15(d)

Dispositions (Narrative) (Details)

v3.20.1
Dispositions (Narrative) (Details)
1 Months Ended 3 Months Ended 12 Months Ended
Jul. 31, 2019
USD ($)
Apr. 30, 2017
USD ($)
Nov. 30, 2006
Dec. 31, 2019
USD ($)
Sep. 30, 2019
USD ($)
Jun. 30, 2019
USD ($)
Mar. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Sep. 30, 2018
USD ($)
Jun. 30, 2018
USD ($)
Mar. 31, 2018
USD ($)
Dec. 31, 2019
USD ($)
item
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2015
item
Business Acquisition [Line Items]                              
Proceeds from sale of crude oil and natural gas properties                           $ 250,000  
Liability for the potential payment $ 4,400,000                            
Income (loss) from discontinued operations, net of tax       $ (37,000) $ (61,000) $ (162,000) $ 5,671,000 $ (80,000) $ (21,000) $ (343,000) $ (52,000) $ 5,411,000 $ (496,000) (621,000)  
Joint Operating With Republic Of Angola [Member]                              
Business Acquisition [Line Items]                              
Joint operation agreement related to third party in working interest percentage     40.00%                        
Additional joint operation agreement related to third party in working interest percentage     10.00%                        
Number of wells drilled | item                             1
Number of drilled wells required by agreement | item                       3      
Stipulated payment for each exploration well, under PSA terms                       $ 10,000,000.0      
Drilling commitment, net       $ 5,000,000.0               5,000,000.0      
Liability for the potential payment               $ 15,000,000.0         15,000,000.0    
East Poplar Dome Field [Member]                              
Business Acquisition [Line Items]                              
Proceeds from sale of crude oil and natural gas properties   $ 300,000                          
Gain from sale of property                           300,000  
Discontinued Operations [Member] | Joint Operating With Republic Of Angola [Member]                              
Business Acquisition [Line Items]                              
Liability for the potential payment             4,500,000                
Write off of receivable             3,300,000                
Income (loss) from discontinued operations, net of tax             $ 5,700,000         $ 5,411,000 $ (496,000) $ (621,000)  
Payment for settlement $ 4,500,000