Financial Instruments - Marketable Securities (Detail) - USD ($) $ in Thousands |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] | ||
| Marketable securities | $ 49,731 | $ 19,260 |
| Level 1 | ||
| Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] | ||
| Marketable securities | $ 49,731 | $ 19,260 |