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Fair Value of Financial Instruments - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Equity securities
Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Realized gain on available-for-sale securities $ 1,557,000  
Available-for-Sale Securities, Fair Value   $ 10,600,000