Statements of Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Statement Of Income And Comprehensive Income [Abstract] | |||
| Unrealized (loss) gain arising during holding period, tax benefit | $ 0 | $ 32 | $ 0 |