Stock-Based Compensation - Restricted Stock Awards (Details) - Restricted Stock Awards - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Number of Shares | ||
| Unvested, beginning balance (shares) | 16 | |
| Granted (shares) | 0 | |
| Vested (shares) | (2) | |
| Forfeited (shares) | 0 | |
| Unvested, ending balance (shares) | 14 | |
| Weighted-Average Grant Date Fair Value per Share | ||
| Unvested, beginning balance (usd per share) | $ 20.93 | |
| Granted (usd per share) | 0.00 | |
| Vested (usd per share) | 5.64 | |
| Forfeited (usd per share) | 0.00 | |
| Unvested, ending balance (usd per share) | $ 22.55 | |
| Stock-based compensation expense | $ 83 | $ 101 |
| Remaining stock-based compensation expense for unvested shares, not yet recognized | $ 102 | |
| Stock-based compensation expense, weighted average recognition period | 5 months 9 days | |
| Employee | ||
| Weighted-Average Grant Date Fair Value per Share | ||
| Vesting period | 4 years | |
| Non-Employee Director | ||
| Weighted-Average Grant Date Fair Value per Share | ||
| Vesting period | 1 year | |