Fair Value of Financial Instruments - Changes in Level 3 Financial Instruments (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
|
| Fair Value Disclosures [Abstract] | ||||
| Transfers into Level 3 | $ 0 | $ 0 | $ 0 | $ 0 |
| Transfers out of Level 3 | $ 0 | $ 0 | $ 0 | $ 0 |