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Marketable Securities, Available for Sale - Additional Information (Detail)
9 Months Ended
Sep. 30, 2015
USD ($)
Investments Debt And Equity Securities [Abstract]  
Available-for-sale securities maturing outside of one year $ 500,000
Realized gains or losses on sales of available-for-sale securities 0
Available-for-sale securities in a continuous material unrealized loss position longer than one year $ 0