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Summary of Gross Realized Gain and Loss from Sale of Available-for-Sale Marketable Securities (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]        
Gross realized gain from sale of available-for-sale marketable securities   $ 20 $ 2 $ 89
Gross realized loss from sale of available-for-sale marketable securities $ (28) $ (21) $ (76) $ (74)