Derivative Instruments - Commodity derivatives (Details) - Swaps	Sep. 30, 2018 bbl / d MMBTU / d $ / bbl $ / gal $ / MMBTU
Natural gas | Three months ending December 31, 2018
Derivative Instruments
Notional amount (MMBtu/Bbls per day)	2,002,500
Natural gas | NYMEX | Three months ending December 31, 2018
Derivative Instruments
Notional amount (MMBtu/Bbls per day)	2,002,500
Weighted average index price | $ / MMBTU	3.53
Natural gas | NYMEX | Year ending December 31, 2019
Derivative Instruments
Notional amount (MMBtu/Bbls per day)	2,330,000
Weighted average index price | $ / MMBTU	3.50
Natural gas | NYMEX | Year ending December 31, 2020
Derivative Instruments
Notional amount (MMBtu/Bbls per day)	1,417,500
Weighted average index price | $ / MMBTU	3.25
Natural gas | NYMEX | Year Ending December 31, 2021
Derivative Instruments
Notional amount (MMBtu/Bbls per day)	710,000
Weighted average index price | $ / MMBTU	3.00
Natural gas | NYMEX | Year ending December 31, 2022
Derivative Instruments
Notional amount (MMBtu/Bbls per day)	850,000
Weighted average index price | $ / MMBTU	3.00
Natural gas | NYMEX | Year ending December 31, 2023
Derivative Instruments
Notional amount (MMBtu/Bbls per day)	90,000
Weighted average index price | $ / MMBTU	2.91
Natural gas liquids | Three months ending December 31, 2018
Derivative Instruments
Notional amount (MMBtu/Bbls per day) | bbl / d	26,000
Propane | Mont Belvieu-Propane | Three months ending December 31, 2018
Derivative Instruments
Notional amount (MMBtu/Bbls per day) | bbl / d	26,000
Weighted average index price | $ / gal	0.77
Oil | Three months ending December 31, 2018
Derivative Instruments
Notional amount (MMBtu/Bbls per day) | bbl / d	6,000
Oil | WTI-NYMEX member | Three months ending December 31, 2018
Derivative Instruments
Notional amount (MMBtu/Bbls per day) | bbl / d	6,000
Weighted average index price | $ / bbl	56.99