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Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Property Plant And Equipment [Abstract]    
Proved oil and gas properties $ 2,418,598 $ 2,271,711
Less: Accumulated depreciation, depletion, amortization and impairment (433,371) (383,564)
Proved oil and gas properties, net 1,985,227 1,888,147
Unproved oil and gas properties 68,600 76,417
Total oil and gas properties, net 2,053,827 1,964,564
Other property and equipment 136,676 49,732
Less: Accumulated depreciation (13,295) (7,696)
Other property and equipment, net 123,381 42,036
Total property, plant and equipment, net $ 2,177,208 $ 2,006,600