Summary of Significant Accounting Policies - Schedule of Components of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Other Comprehensive Income Loss Tax Parenthetical Disclosures [Abstract] | |||
| Tax on Unrealized gain (loss) on investments before reclassification | $ (14) | $ 20 | $ 47 |
| Tax on Reclassification adjustment for net losses realized in net income | $ 8 | ||