Annual report pursuant to Section 13 and 15(d)

Schedule of Depreciation, Depletion, Amortization and Accretion Expense (Detail)

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Schedule of Depreciation, Depletion, Amortization and Accretion Expense (Detail)
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Reserve Quantities [Line Items]      
Depreciation, depletion, amortization and accretion per Mcfe 4.18 3.47 3.24