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