Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies - Additional Information (Detail)

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Commitments and Contingencies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 6 Months Ended 1 Months Ended 3 Months Ended 6 Months Ended 48 Months Ended
Jun. 30, 2013
Well
Dec. 31, 2012
Jun. 30, 2013
Offshore Gabon [Member]
Sqkms
Well
Jan. 31, 2007
Angola [Member]
Sqkms
Nov. 30, 2006
Angola [Member]
Well
Jun. 30, 2013
Angola [Member]
Dec. 31, 2008
Angola [Member]
Sqkms
Jun. 30, 2013
Angola [Member]
acre
Nov. 01, 2010
Angola [Member]
Sqkms
Jun. 30, 2012
Angola [Member]
Long-term Purchase Commitment [Line Items]                    
Cost for acquire property     $ 5.3              
Length of acquired property     150              
Number of exploration wells     2   2          
Cost related to drilling     8.6              
Cost related to share of drilling     2.6              
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%    
Full allowance against accounts receivable from partners 7.2 6.0                
Allowance recorded for accounts receivable with remainder           $ 0.3   $ 1.1