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, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
|
Investments, Debt and Equity Securities [Abstract] | ||||
Gross realized gains from sale of available-for-sale marketable securities | $ 1 | $ 16 | $ 2 | |
Gross realized losses from sale of available-for-sale marketable securities | $ (1) | $ (28) | $ (32) | $ (76) |