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Fair Value of Financial Instruments - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Financial Instruments [Line Items]    
Realized gain on available-for-sale securities $ 1,557,000  
Debt, fair value 381,500,000 76,800,000
Debt, carrying value 374,300,000 75,000,000
Equity Securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
   
Financial Instruments [Line Items]    
Available For Sale Securities , Fair Value   $ 10,600,000