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Derivatives, Hedges, Financial Instruments and Carbon Credits - Additional Information (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified
 1 Months Ended 12 Months Ended
Feb. 28, 2011
Sep. 30, 2008
Apr. 30, 2008
Dec. 31, 2013
MMBTU
Unit
lb
Dec. 31, 2012
lb
Derivative Instruments and Hedging Activities Disclosures [Line Items]          
Contractual weighted-average pay rate       3.23%  
Estimated market weighted-average receive rate       0.54%  
Carbon credit fair value per unit       1.00 0.50
Derivative future or forward contracts in pounds         625,000
Derivative future or forward contracts in volume       1,530,000  
Future or forward copper contracts period       October 2014 May 2013
Weighted-average cost per pound of future or forward copper contracts       3.98 3.53
Interest rate contracts fixed rate description Fixed three-month LIBOR rate of 3.23% on a declining balance Fixed three-month LIBOR rate of 3.595% on $25 million Fixed three-month LIBOR rate of 3.24% on $25 million    
Maturity period interest rate contracts held March 2016 April 2012 April 2012    
Interest rate contracts at cost basis   $ 0.4      
LIBOR rate 3.23% 3.595% 3.24%    
Interest rate swap declining balance beginning balance 23.8 25.0 25.0    
Interest rate swap declining balance ending balance 18.8        
Number of carbon credits       1,284,000  
Assets or liabilities measured at fair value on a recurring basis transferred between Level 1 and Level 2 classifications           
Senior Secured Notes [Member]
          
Derivative Instruments and Hedging Activities Disclosures [Line Items]          
Excess of estimated fair value over carrying value       $ 20  
Senior Secured Notes [Member] | Significant Other Observable Inputs (Level 2) [Member]
          
Derivative Instruments and Hedging Activities Disclosures [Line Items]          
Notes lower range of ask or bid price       $ 104.5  
Notes higher range of ask or bid price       $ 104.9