Derivative Instruments - Summary of Derivative Instruments (Details) - Crude Oil	Sep. 30, 2019 ThousandBarrels / d $ / Barrel
2019 Settlement
Derivative [Line Items]
Derivative instruments (mmbls/day) | ThousandBarrels / d	8,000.0
2019 Settlement | Short position
Derivative [Line Items]
Ceiling sold price (dollars per barrel)	72.98
Purchase price (dollars per barrel)	46.72
2019 Settlement | Long position
Derivative [Line Items]
Purchase price (dollars per barrel)	56.72
2020 Settlement
Derivative [Line Items]
Derivative instruments (mmbls/day) | ThousandBarrels / d	109,800
2020 Settlement | Short position
Derivative [Line Items]
Ceiling sold price (dollars per barrel)	74.09
Purchase price (dollars per barrel)	45.00
2020 Settlement | Long position
Derivative [Line Items]
Purchase price (dollars per barrel)	55.00
2021 Settlement
Derivative [Line Items]
Derivative instruments (mmbls/day) | ThousandBarrels / d	109,500
2021 Settlement | Short position
Derivative [Line Items]
Ceiling sold price (dollars per barrel)	74.09