Fair Value Measurements - Additional Information (Details) - USD ($) |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
|
| Fair Value Disclosures [Abstract] | ||||
| Transfers between fair value measure levels | $ 0 | $ 0 | $ 0 | $ 0 |