Annual report pursuant to Section 13 and 15(d)

Disposition of Assets - Additional Information (Detail)

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Disposition of Assets - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Component of Other Expense, Nonoperating [Line Items]      
Asset dispositions, proceeds $ 200,000 $ 0 $ 0
Asset dispositions, loss 500,000    
Provision for reduction in carrying value of certain assets $ 0 $ 1,350,000 $ 1,952,000