Net Loss Per Share - Schedule of Potential Common Shares Issuable Upon Conversion of Warrants (Details) - shares |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Potential common shares | |||
| Total (in shares) | 2,833,619 | 2,225,648 | 12,137,409 |
| Stock options to purchase common stock | |||
| Potential common shares | |||
| Total (in shares) | 2,657,187 | 2,128,346 | 1,569,379 |
| Stock warrants to purchase common stock | |||
| Potential common shares | |||
| Total (in shares) | 176,432 | 97,302 | 650,618 |
| Redeemable convertible preferred stock | |||
| Potential common shares | |||
| Total (in shares) | 0 | 0 | 9,890,580 |
| Redeemable convertible preferred stock warrants | |||
| Potential common shares | |||
| Total (in shares) | 0 | 0 | 26,832 |