Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies - Additional Information (Detail)

v2.4.0.8
Commitments and Contingencies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 9 Months Ended 1 Months Ended 3 Months Ended 9 Months Ended 1 Months Ended 3 Months Ended 48 Months Ended
Sep. 30, 2013
Dec. 31, 2012
Sep. 30, 2013
Offshore Gabon
Well
Sep. 30, 2013
Offshore Gabon
Omangou Prospect
Well
Sep. 30, 2013
Offshore Gabon
Ovoka Well
Well
Sep. 30, 2013
Offshore Gabon
Seismic Obligation
Sqkms
Nov. 30, 2006
Angola
Well
Sep. 30, 2013
Angola
Sep. 30, 2013
Angola
Well
acre
Jun. 30, 2012
Angola
Jan. 31, 2007
Angola
Seismic Obligation
Sqkms
Dec. 31, 2008
Angola
Seismic Obligation
Sqkms
Nov. 01, 2010
Angola
Seismic Obligation
Sqkms
Long Term Purchase Commitment [Line Items]                          
Cost for acquire property     $ 5.3                    
Length of acquired property           150              
Number of exploration wells     2 1 1   2            
Cost related to drilling       8.6 19.8                
Cost related to share of drilling       2.6 6.0                
Acquisition related to obligation           223              
Number of exploration wells drilling required to pay remaining obligation         1                
Annual funding related to production license, term     7 years                    
Percentage of annual funding over seven years     12.14%                    
Percentage of annual funding over last three years     5.00%                    
Abandonment cost related to annual funding     10.1                    
Area under property exploration rights                 1,400,000        
Joint operation agreement related to third party in working interest percentage               40.00% 40.00%        
Additional joint operation agreement related to third party in working interest percentage                 10.00%        
Production license agreement term             4 years            
Production license agreement term extended by government             3 years            
Length of acquired data                     1,175 524 1,000
Drilling cost to company             14.8            
Seismic obligation cost to company                     3.75 3.00  
Cost related to seismic obligation, gross                     7.5 6.0  
Cost related to drilling             29.5            
Well penalty, minimum 5.0                        
Well penalty, maximum 10.0                        
Recorded restricted cash 10.0                        
Percentage of working interest for amounts owned               40.00% 40.00% 40.00%      
Percentage of carried interest               10.00% 10.00%        
Allowance for accounts with partners 7.4 6.0           7.4 7.4        
Allowance recorded for accounts receivable with remainder               $ 0.1 $ 1.3        
Number of exploration wells intended for drilling after working interest assignment completed                 2