Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies (Details)

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Commitments and Contingencies (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 1 Months Ended 3 Months Ended 48 Months Ended
Mar. 31, 2013
Well
Dec. 31, 2012
Mar. 31, 2013
Offshore Gabon [Member]
Well
sqkm
Jan. 31, 2007
Angola [Member]
sqkm
Nov. 30, 2006
Angola [Member]
Well
Mar. 31, 2013
Angola [Member]
acre
Dec. 31, 2008
Angola [Member]
sqkm
Nov. 01, 2010
Angola [Member]
sqkm
Long-term Purchase Commitment [Line Items]                
Drilling cost to company         $ 14.8      
Cost related to seismic obligation, gross       7.5     6.0  
Seismic obligation cost to company       3.75     3.00  
Length of acquired property     150          
Cost for acquire property     5.3          
Number of exploration wells     2   2      
Cost related to drilling     8.6          
Cost related to drilling, gross         29.5      
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     9.7          
Length of acquired data       1,175     524 1,000
Production license agreement term         4 years      
Production license agreement term extended by government         3 years      
Area under acquire property exploration rights agreement term           1,400,000    
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%    
Percentage of working interest acquired           40.00%    
Percentage of carried interest           10.00%    
Full allowance against accounts receivable from partners 6.9 6.0            
Percentage of working interest for amounts owned           40.00%    
Commitments and Contingencies (Textual) [Abstract]                
Well penalty, minimum 5.0              
Well penalty, maximum 10.0              
Recorded restricted cash 10.0              
Allowance recorded for accounts receivable with remainder           $ 0.9