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Cash, Cash Equivalents and Short-Term Investments - Additional Information (Detail) (Maximum [Member])
 9 Months Ended 12 Months Ended
Sep. 30, 2013
Dec. 31, 2012
Dec. 31, 2011
Maximum [Member]
      
Cash and Cash Equivalents [Line Items]      
Short term investment maturity period 1 year 1 year 1 year