Industrial Revenue Bond (Detail) - Summary of Financial Assets and Liabilities that are Offset (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Gross Amounts Of Recognized Assets Liabilities [Member]
Offsetting Assets and Liabilities [Line Items]
Investment in bonds	$ 7,000	$ 7,000
Capital lease obligation	(7,000)	(7,000)
Gross Amounts Off Set In The Balance Sheet [Member]
Offsetting Assets and Liabilities [Line Items]
Investment in bonds	7,000	7,000
Capital lease obligation	(7,000)	(7,000)
Net Amounts Of Assets Liabilities Presented In The Balance Sheet [Member]
Offsetting Assets and Liabilities [Line Items]
Investment in bonds	0	0
Capital lease obligation	$ 0	$ 0