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Cash, Cash Equivalents and Marketable Securities - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Schedule of Available-for-sale Securities [Line Items]        
Realized gains or losses from the sale of marketable securities $ 0 $ 0 $ 0 $ 0