Derivative Instruments - Gains and Losses from Derivative Instruments (Details) - USD ($) $ in Thousands |
3 Months Ended | |
|---|---|---|
Mar. 31, 2019 |
Mar. 31, 2018 |
|
| Derivative Instruments and Hedging Activities Disclosure [Abstract] | ||
| Net gain (loss) on derivative instruments | $ (5,871) | $ 7,843 |