Summary of Gross Realized Gain and Loss from Sale of Available-for-Sale Marketable Securities (Detail) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Investments, Debt and Equity Securities [Abstract] | |||
| Gross realized gains from sale of available-for-sale marketable securities | $ 24 | $ 4 | $ 99 |
| Gross realized losses from sale of available-for-sale marketable securities | $ (33) | $ (82) | $ (93) |