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Basis of Presentation - Additional Information (Detail)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2016
USD ($)
Jun. 30, 2015
USD ($)
Mar. 31, 2015
USD ($)
Jun. 30, 2016
USD ($)
Project
Jun. 30, 2015
USD ($)
Mar. 31, 2016
USD ($)
Significant Accounting Policies [Line Items]            
Number of projects suspended | Project       2    
Percentage of suspended projects relating to two projects       90.00%    
Projects completed percentage       90.00%    
Lower of cost or market inventory adjustment     $ 4,372   $ 4,372  
Production cost $ 13,515 $ 11,208   $ 23,222 $ 19,629  
Bauxite raw materials            
Significant Accounting Policies [Line Items]            
Impairment of long-term portion of the bauxite raw material           $ 1,065