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Segment Information - Segment Financial Information (Parenthetical) (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Mar. 31, 2014
Sep. 30, 2015
Sep. 30, 2014
Segment Reporting Information [Line Items]          
Impairment of natural gas properties $ 39,670     $ 39,670  
Interest cost capitalized 8,300 $ 3,900   $ 20,900 $ 9,200
Chemical [Member]          
Segment Reporting Information [Line Items]          
Business interruption and property insurance recoveries     $ 28,000    
Impairment of natural gas properties $ 39,700        
Cost of Sales [Member] | Chemical [Member]          
Segment Reporting Information [Line Items]          
Business interruption loss     $ 22,900