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Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Property, Plant and Equipment [Line Items]    
Proved oil and gas properties $ 2,271,711 $ 1,152,532
Less: Accumulated depreciation, depletion, amortization and impairment (383,564) (174,948)
Proved oil and gas properties, net 1,888,147 977,584
Unproved oil and gas properties 76,417 82,825
Other property and equipment 49,732 20,859
Less: Accumulated depreciation (7,696) (1,313)
Other property and equipment, net 42,036 19,546
Total property, plant and equipment, net $ 2,006,600 $ 1,079,955