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Property, Plant and Equipment - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Mar. 05, 2014
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Dec. 31, 2014
Property, Plant and Equipment [Line Items]            
Impairment of oil and gas properties   $ 80,000 $ 1,439,000 $ 24,917,000 $ 2,243,000  
Gain on sale of properties   172,000 43,000 172,000 187,076,000  
Unproved property leases [Member]            
Property, Plant and Equipment [Line Items]            
Impairment of oil and gas properties   100,000 1,400,000 24,900,000 2,200,000  
Impairment of oil and gas properties, periodic assessments       16,400,000    
Proved Oil And Gas Properties [Member]            
Property, Plant and Equipment [Line Items]            
Impairment of oil and gas properties   $ 0 $ 0 $ 0 $ 0  
Non-Operated Oil and Natural Gas Properties [Member]            
Property, Plant and Equipment [Line Items]            
Proceeds from sale of properties $ 324,900,000          
Gain on sale of properties           $ 187,000,000