Marketable Investments - Summary of Company's Marketable Investments (Detail) - USD ($) $ in Thousands |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Schedule of Available-for-sale Securities [Line Items] | ||
| Amortized Cost | $ 61,281 | |
| Gross Unrealized Gains | 2 | |
| Gross Unrealized Losses | (136) | |
| Market Value | 61,147 | $ 47,775 |
| Federal Agency Obligations [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Amortized Cost | 1,800 | |
| Gross Unrealized Losses | (7) | |
| Market Value | 1,793 | |
| Corporate Obligations [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Amortized Cost | 59,481 | 47,939 |
| Gross Unrealized Gains | 2 | |
| Gross Unrealized Losses | (129) | (164) |
| Market Value | $ 59,354 | $ 47,775 |