Quarterly report pursuant to Section 13 or 15(d)

Segment Information - Segment Activity (Detail)

v2.4.0.8
Segment Information - Segment Activity (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Dec. 31, 2012
Segment Reporting Information [Line Items]          
Revenues, Net $ 29,118 $ 58,818 $ 73,255 $ 104,104  
Income from operations 11,666 38,632 33,170 68,739  
Total assets 272,223   272,223   267,956
Operating Segments [Member] | Corporate and Other [Member]
         
Segment Reporting Information [Line Items]          
Revenues, Net             
Income from operations (1,307) (2,198) (3,482) (5,061)  
Total assets 26,846   26,846   38,585
Operating Segments [Member] | Gabon [Member]
         
Segment Reporting Information [Line Items]          
Revenues, Net 28,574 57,886 72,229 102,613  
Income from operations 14,853 45,258 45,717 79,605  
Total assets 208,545   208,545   190,652
Operating Segments [Member] | Angola [Member]
         
Segment Reporting Information [Line Items]          
Revenues, Net              
Income from operations (379) (585) (1,582) (1,199)  
Total assets 12,126   12,126   11,405
Operating Segments [Member] | Equatorial Guinea [Member]
         
Segment Reporting Information [Line Items]          
Revenues, Net              
Income from operations (165)    (455)     
Total assets 10,010   10,010   10,000
Operating Segments [Member] | USA [Member]
         
Segment Reporting Information [Line Items]          
Revenues, Net 544 932 1,026 1,491  
Income from operations (1,336) (3,843) (7,028) (4,606)  
Total assets $ 14,696   $ 14,696   $ 17,314