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Changes to Company's Asset Retirement Obligations (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Reconciliation of Changes in Asset Retirement Obligations [Line Items]    
Balance at beginning of year $ 4,422 $ 3,455
Liabilities incurred 375 418
Liabilities settled (126) (150)
Accretion expense 166 163
Revision in estimated costs of plugging oil and natural gas wells   536
Asset retirement obligation at end of year $ 4,837 $ 4,422