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Supplemental Oil Reserve Information (Unaudited) - Additional Information (Detail)
Dec. 31, 2012
bbl
Dec. 31, 2011
bbl
Dec. 31, 2010
bbl
Reserve Quantities [Line Items]      
Proved developed reserves 2,927,000 2,714,150 2,320,150
Proved Developed Reserves
     
Reserve Quantities [Line Items]      
Proved developed reserves 1,546.3 643.1  
Proved Undeveloped Reserve [Member]
     
Reserve Quantities [Line Items]      
Proved developed reserves 1,380.8 2,071.1