Fair Value of Financial Instruments - Transfers (Details) - USD ($) $ in Thousands |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Fair Value of Financial Instrument | ||
| Fair value assets, transfers from level 1 to level 2 | $ 0 | $ 0 |
| Fair value assets, transfers from level 2 to level 1 | 0 | 0 |
| Fair value liabilities, transfers from level 1 to level 2 | 0 | 0 |
| Fair value liabilities, transfers from level 2 to level 1 | 0 | 0 |
| Fair value assets, transfers into level 3 | 0 | 0 |
| Fair value assets, transfers out of level 3 | 0 | 0 |
| Fair value liabilities, transfers into level 3 | 0 | 0 |
| Fair value liabilities, transfers out of level 3 | $ 0 | $ 0 |