Construction in Progress - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2014 acre
Property, Plant and Equipment [Line Items]
Construction project completion year	2013
Area of land	81,561
Percentage for smelting equipment	25.00%
First Phase Of Construction Project
Property, Plant and Equipment [Line Items]
Construction project completion year	2011
Second Phase Of Construction Project
Property, Plant and Equipment [Line Items]
Construction project completion year	2012