Derivative Financial Instruments (Details) bbl in Thousands, BTU in Billions		Nov. 02, 2018 BTU $ / EnergyContent $ / Barrels bbl	Sep. 30, 2018 BTU $ / EnergyContent $ / Barrels bbl
NYMEX Oil Swap Contract Fourth Quarter 2018 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			1,894
Derivative, Swap Type, Average Fixed Price | $ / Barrels			49.87
NYMEX Oil Swap Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			3,733
Derivative, Swap Type, Average Fixed Price | $ / Barrels			59.80
NYMEX Oil Swap Contract 2020 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			2,491
Derivative, Swap Type, Average Fixed Price | $ / Barrels			65.68
NYMEX Oil Swap Contracts [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			8,118
NYMEX Oil Collar Contract Fourth Quarter 2018 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			2,222
Derivative, Floor Price | $ / Barrels			50.00
Derivative, Ceiling Price | $ / Barrels			58.44
NYMEX Oil Collar Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			10,055
Derivative, Floor Price | $ / Barrels			50.59
Derivative, Ceiling Price | $ / Barrels			63.62
NYMEX Oil Collar Contract 2020 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			1,165
Derivative, Floor Price | $ / Barrels			55.00
Derivative, Ceiling Price | $ / Barrels			66.47
NYMEX Oil Collar Contracts [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			13,442
Gas Swaps Contract Fourth Quarter 2018 [Member]
Derivative Financial Instruments
Derivative, Swap Type, Average Fixed Price | $ / EnergyContent			3.27
Derivative, Nonmonetary Notional Amount, Energy Measure | BTU			28,204
Derivative, Nonmonetary Notional Amount, Energy Measure, Purchased Volumes | BTU			(7,210)
Derivative, Swap Type, Weighted-Average Fixed Price, Purchased Volumes | $ / EnergyContent			4.27
Derivative, Nonmonetary Notional Amount, Energy Measure, Net Volumes | BTU			20,994
Derivative, Swap Type, Average Fixed Price, Net of Purchased Volumes | $ / EnergyContent			2.92
Gas Swaps Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Swap Type, Average Fixed Price | $ / EnergyContent			3.58
Derivative, Nonmonetary Notional Amount, Energy Measure | BTU			50,021
Derivative, Nonmonetary Notional Amount, Energy Measure, Purchased Volumes | BTU			(24,415)
Derivative, Swap Type, Weighted-Average Fixed Price, Purchased Volumes | $ / EnergyContent			4.34
Derivative, Nonmonetary Notional Amount, Energy Measure, Net Volumes | BTU			25,606
Derivative, Swap Type, Average Fixed Price, Net of Purchased Volumes | $ / EnergyContent			2.85
Gas Swaps Contract 2020 [Member]
Derivative Financial Instruments
Derivative, Swap Type, Average Fixed Price | $ / EnergyContent			2.82
Derivative, Nonmonetary Notional Amount, Energy Measure | BTU			2,942
Derivative, Nonmonetary Notional Amount, Energy Measure, Purchased Volumes | BTU			0
Derivative, Swap Type, Weighted-Average Fixed Price, Purchased Volumes | $ / EnergyContent			0.00
Derivative, Nonmonetary Notional Amount, Energy Measure, Net Volumes | BTU			2,942
Derivative, Swap Type, Average Fixed Price, Net of Purchased Volumes | $ / EnergyContent			2.82
Gas Swaps Contracts [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Energy Measure | BTU			81,167
Derivative, Nonmonetary Notional Amount, Energy Measure, Purchased Volumes | BTU			(31,625)
Derivative, Nonmonetary Notional Amount, Energy Measure, Net Volumes | BTU			49,542
IF HSC Gas Collar Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Floor Price | $ / EnergyContent			2.50
Derivative, Ceiling Price | $ / EnergyContent			2.83
Derivative, Nonmonetary Notional Amount, Energy Measure | BTU			14,242
WTI Midland NYMEX WTI [Member] | Oil Basis Swap Contract Fourth Quarter 2018 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			3,327
Weighted-Average Contract Price | $ / Barrels	[1]		(1.08)
WTI Midland NYMEX WTI [Member] | Oil Basis Swap Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			11,217
Weighted-Average Contract Price | $ / Barrels	[1]		(3.36)
WTI Midland NYMEX WTI [Member] | Oil Basis Swap Contract 2020 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			10,960
Weighted-Average Contract Price | $ / Barrels	[1]		(1.05)
WTI Midland NYMEX WTI [Member] | Oil Basis Swap Contract 2021 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			0
Weighted-Average Contract Price | $ / Barrels	[1]		0.00
WTI Midland NYMEX WTI [Member] | Oil Basis Swap Contract 2022 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			0
Weighted-Average Contract Price | $ / Barrels	[1]		0.00
WTI Midland NYMEX WTI [Member] | Oil Basis Swap [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			25,504
NYMEX WTI ICE Brent [Member] | Oil Basis Swap Contract Fourth Quarter 2018 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			0
Weighted-Average Contract Price | $ / Barrels	[2]		0.00
NYMEX WTI ICE Brent [Member] | Oil Basis Swap Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			0
Weighted-Average Contract Price | $ / Barrels	[2]		0.00
NYMEX WTI ICE Brent [Member] | Oil Basis Swap Contract 2020 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			1,840
Weighted-Average Contract Price | $ / Barrels	[2]		(8.01)
NYMEX WTI ICE Brent [Member] | Oil Basis Swap Contract 2021 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			3,650
Weighted-Average Contract Price | $ / Barrels	[2]		(7.86)
NYMEX WTI ICE Brent [Member] | Oil Basis Swap Contract 2022 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			3,650
Weighted-Average Contract Price | $ / Barrels	[2]		(7.78)
NYMEX WTI ICE Brent [Member] | Oil Basis Swap [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			9,140
OPIS Ethane Purity Mont Belvieu [Member] | NGL Swaps Contract Fourth Quarter 2018 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			1,146
Derivative, Swap Type, Average Fixed Price | $ / Barrels			11.18
OPIS Ethane Purity Mont Belvieu [Member] | NGL Swaps Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			3,533
Derivative, Swap Type, Average Fixed Price | $ / Barrels			12.31
OPIS Ethane Purity Mont Belvieu [Member] | NGL Swaps Contract 2020 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			539
Derivative, Swap Type, Average Fixed Price | $ / Barrels			11.13
OPIS Ethane Purity Mont Belvieu [Member] | NGL Swaps Contracts [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			5,218
OPIS Propane Mont Belvieu Non-TET [Member] | NGL Swaps Contract Fourth Quarter 2018 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			671
Derivative, Swap Type, Average Fixed Price | $ / Barrels			24.39
OPIS Propane Mont Belvieu Non-TET [Member] | NGL Swaps Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			1,980
Derivative, Swap Type, Average Fixed Price | $ / Barrels			28.89
OPIS Propane Mont Belvieu Non-TET [Member] | NGL Swaps Contract 2020 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			0
Derivative, Swap Type, Average Fixed Price | $ / Barrels			0.00
OPIS Propane Mont Belvieu Non-TET [Member] | NGL Swaps Contracts [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			2,651
OPIS Normal Butane Mont Belvieu Non-TET [Member] | NGL Swaps Contract Fourth Quarter 2018 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			102
Derivative, Swap Type, Average Fixed Price | $ / Barrels			35.70
OPIS Normal Butane Mont Belvieu Non-TET [Member] | NGL Swaps Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			154
Derivative, Swap Type, Average Fixed Price | $ / Barrels			35.64
OPIS Normal Butane Mont Belvieu Non-TET [Member] | NGL Swaps Contract 2020 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			0
Derivative, Swap Type, Average Fixed Price | $ / Barrels			0.00
OPIS Normal Butane Mont Belvieu Non-TET [Member] | NGL Swaps Contracts [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			256
OPIS Isobutane Mont Belvieu Non-TET [Member] | NGL Swaps Contract Fourth Quarter 2018 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			76
Derivative, Swap Type, Average Fixed Price | $ / Barrels			35.07
OPIS Isobutane Mont Belvieu Non-TET [Member] | NGL Swaps Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			117
Derivative, Swap Type, Average Fixed Price | $ / Barrels			35.70
OPIS Isobutane Mont Belvieu Non-TET [Member] | NGL Swaps Contract 2020 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			0
Derivative, Swap Type, Average Fixed Price | $ / Barrels			0.00
OPIS Isobutane Mont Belvieu Non-TET [Member] | NGL Swaps Contracts [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			193
OPIS Natural Gasoline Mont Belvieu Non-TET [Member] | NGL Swaps Contract Fourth Quarter 2018 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			208
Derivative, Swap Type, Average Fixed Price | $ / Barrels			50.99
OPIS Natural Gasoline Mont Belvieu Non-TET [Member] | NGL Swaps Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			197
Derivative, Swap Type, Average Fixed Price | $ / Barrels			50.93
OPIS Natural Gasoline Mont Belvieu Non-TET [Member] | NGL Swaps Contract 2020 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			0
Derivative, Swap Type, Average Fixed Price | $ / Barrels			0.00
OPIS Natural Gasoline Mont Belvieu Non-TET [Member] | NGL Swaps Contracts [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume			405
Subsequent Event [Member] | Gas Swaps Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Energy Measure | BTU		15,769
Subsequent Event [Member] | NYMEX WTI ICE Brent [Member] | Oil Basis Swap Contract 2020 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume		900
Subsequent Event [Member] | OPIS Propane Mont Belvieu Non-TET [Member] | NGL Swaps Contract Fourth Quarter 2018 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume		100
Derivative, Swap Type, Average Fixed Price | $ / Barrels		45.59
Subsequent Event [Member] | OPIS Propane Mont Belvieu Non-TET [Member] | NGL Swaps Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Nonmonetary Notional Amount, Volume		400
Derivative, Swap Type, Average Fixed Price | $ / Barrels		40.11
Minimum [Member] | Subsequent Event [Member] | Gas Swaps Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Swap Type, Average Fixed Price | $ / EnergyContent		2.80
Minimum [Member] | Subsequent Event [Member] | NYMEX WTI ICE Brent [Member] | Oil Basis Swap Contract 2020 [Member]
Derivative Financial Instruments
Weighted-Average Contract Price | $ / Barrels		(8.05)
Maximum [Member] | Subsequent Event [Member] | Gas Swaps Contract 2019 [Member]
Derivative Financial Instruments
Derivative, Swap Type, Average Fixed Price | $ / EnergyContent		3.42
Maximum [Member] | Subsequent Event [Member] | NYMEX WTI ICE Brent [Member] | Oil Basis Swap Contract 2020 [Member]
Derivative Financial Instruments
Weighted-Average Contract Price | $ / Barrels		(8.10)

[1] (1) Represents the price differential between WTI Midland (Midland, Texas) and NYMEX WTI (Cushing, Oklahoma).

[2] (2) Represents the price differential between NYMEX WTI (Cushing, Oklahoma) and ICE Brent (North Sea).