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Oil and Gas Reserves Information (Unaudited) - Summary of Changes in Net Quantities of Crude Oil and Natural Gas Reserves (Detail)
12 Months Ended
Dec. 31, 2016
MBbls
MMcf
Dec. 31, 2015
MBbls
MMcf
Dec. 31, 2014
MBbls
MMcf
Dec. 31, 2013
MBbls
MMcf
Oil (MBbls)        
Proved Reserves:        
Beginning of year | MBbls 9,229 20,854 21,976  
Revisions of previous estimates | MBbls (406) (5,096) (2,182)  
Extensions and discoveries | MBbls 64 231 5,373  
Sales of minerals in place | MBbls (222) (3,671)    
Production | MBbls (1,388) (3,089) (4,313)  
End of year | MBbls 7,277 9,229 20,854  
Proved Developed Reserves:        
Proved Developed Reserves | MBbls 7,277 9,229 16,247 13,914
Natural Gas (MMcf)        
Proved Reserves:        
Beginning of year | MMcf 569,596 495,266 452,653  
Revisions of previous estimates | MMcf 130,416 (41,437) 3,998  
Extensions and discoveries | MMcf 285,076 168,539 78,383  
Sales of minerals in place | MMcf (58,942) (5,096)    
Production | MMcf (53,678) (47,676) (39,768)  
End of year | MMcf 872,468 569,596 495,266  
Proved Developed Reserves:        
Proved Developed Reserves | MMcf 321,527 311,130 324,598 344,278