Available-for-Sale Marketable Securities - Schedule of Fair Values and Amortized Cost of Marketable Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Investments, Debt and Equity Securities [Abstract] | ||
| Fair value of marketable debt securities, contractual maturity, Less than one year | $ 37,908 | $ 49,653 |
| Amortized Cost of marketable debt securities, contractual maturity, Less than one year | $ 37,913 | $ 49,657 |