Fair Value of Financial Instruments - Changes in Level 3 Financial Instruments (Details) - USD ($) |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2019 |
Jun. 30, 2018 |
Jun. 30, 2019 |
Jun. 30, 2018 |
|
| Fair Value Disclosures [Abstract] | ||||
| Transfers into Level 3 | $ 0 | $ 0 | $ 0 | $ 0 |
| Transfers out of Level 3 | $ 0 | $ 0 | $ 0 | $ 0 |