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Fair Value Measurements - Additional Information (Detail) (Fair Value, Measurements, Recurring [Member], USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Fair Value, Measurements, Recurring [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Other-than-temporary impairment loss $ 0 $ 0 $ 0