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Property, Plant and Equipment - Additional Information (Detail) (USD $)
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Property, Plant and Equipment [Line Items]      
Asset retirement costs $ 32,600,000 $ 20,700,000  
Impairment of oil and gas properties 1,168,000 3,581,000 3,610,000
Unproved property leases [Member]
      
Property, Plant and Equipment [Line Items]      
Impairment of oil and gas properties $ 1,200,000 $ 3,600,000 $ 3,600,000