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Plant Closure Provisions - Additional Information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Restructuring Cost and Reserve [Line Items]      
Expenditure $ 2.6 $ 2.0 $ 2.0
Remediation [Member]      
Restructuring Cost and Reserve [Line Items]      
Accretion expense recognized 3.0    
Remediation charge for changes in the scope and cost of future remediation activities $ 3.8    
Discount rate of remediation provision 8.92%    
Expenditure $ 2.6 $ 2.0 $ 1.9