Annual report pursuant to Section 13 and 15(d)

Oil And Natural Gas Properties And Equipment (Narrative) (Detail)

v3.3.1.900
Oil And Natural Gas Properties And Equipment (Narrative) (Detail)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2015
USD ($)
Sep. 30, 2015
USD ($)
Jun. 30, 2015
USD ($)
Mar. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Sep. 30, 2014
USD ($)
Jun. 30, 2014
USD ($)
Mar. 31, 2014
USD ($)
Dec. 31, 2015
USD ($)
item
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]                      
Number of fields reviewed for impairment | item                 5    
Fair value of fields $ 412,593       $ 338,641       $ 412,593 $ 338,641  
Impairment of proved properties 52,100 $ 18,000 $ 5,800 $ 5,400 98,300       81,322 98,341  
Impairment Of Oil And Gas Properties 8,800 0 $ 600 2,700 2,300 $ 0 $ 800 $ 800      
Inventory write-off 3,400                    
U.S. Fields [Member]                      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]                      
Fair value of fields 1,200               1,200    
Impairment Of Oil And Gas Properties                 3,200    
Etame Field [Member]                      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]                      
Fair value of fields $ 12,700               12,700    
Impairment Of Oil And Gas Properties                 78,100    
Etame, Ebouri, Southeast Etame and North Tchibala [Member]                      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]                      
Fair value of fields         41,100         41,100  
Impairment Of Oil And Gas Properties                   98,300 $ 0
Roosevelt County, Montana [Member]                      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]                      
Undeveloped leasehold value         $ 1,200         $ 1,200  
Angola [Member]                      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]                      
Impairment Of Oil And Gas Properties                 8,200    
Inventory write-off                 1,900    
Scenario, Adjustment [Member]                      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]                      
Impairment Of Oil And Gas Properties   $ 3,600             $ 7,000    
Kindele #1 [Member]                      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]                      
Impairment Of Oil And Gas Properties       $ 2,800