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Marketable Securities - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2014
Sep. 30, 2014
Dec. 31, 2013
Investments Debt And Equity Securities [Abstract]      
Other-than-temporary impairments of investments $ 0 $ 0 $ 0