Annual report pursuant to Section 13 and 15(d)

Impairment of Proved Properties - Additional Information (Detail)

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Impairment of Proved Properties - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Impairment of Proved Properties (Textual) [Abstract]  
Company recognized an impairment loss $ 7.6