Preferred Stock - Liquidation Preference (Details) - USD ($) $ in Thousands |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Redeemable convertible preferred stock | ||
| Convertible preferred stock | ||
| Liquidation preference of the redeemable convertible preferred stock | $ 272,506 | $ 272,506 |