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Investment in Joint Venture - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Dec. 31, 2012
Nov. 30, 2007
Schedule of Equity Method Investments [Line Items]            
Cash dividends received, recorded as reduction in Company's investment in joint venture       $ 500    
Equity income, net of tax 508 201 860 475    
Dowa - Olin Metal Corporation [Member]
           
Schedule of Equity Method Investments [Line Items]            
Interest in joint venture 50.00%   50.00%      
Carrying value as a result of bargain purchase event           0
Negative basis difference 5,373   5,373   5,735 9,416
Negative basis difference accreted on a straight-line basis Period     13 years      
Accretion of negative basis difference 181 181 362 362    
Cash dividends received, recorded as reduction in Company's investment in joint venture     0 500    
Equity income, net of tax 508 201 860 475    
Undistributed earnings of joint venture in retained earnings $ 922   $ 922   $ 62