Derivative Commodity Instruments - Derivative Transactions (Details) gal in Millions	9 Months Ended
	Sep. 30, 2018 mbbl gal Bcf $ / bbl $ / Mcf $ / gal
2018 | NYMEX Swaps | Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMGal and Bcf) | mbbl	540
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf)	60.25
2018 | NYMEX Three-Way Collars | Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMGal and Bcf) | mbbl	3,375
2018 | Ceiling sold price (call) | Oil | Short
Derivatives, Fair Value [Line Items]
Ceiling sold price (call) (in dollars per Bbl)	60.04
2018 | Floor Purchased and Sold Price (Put) | Oil | Short
Derivatives, Fair Value [Line Items]
Floor purchased and sold price (in dollars per Bbl)	35.47
2018 | Floor Purchased and Sold Price (Put) | Oil | Long
Derivatives, Fair Value [Line Items]
Floor purchased and sold price (in dollars per Bbl)	45.47
2018 | WTI/WTI Basis Swaps | Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMGal and Bcf) | mbbl	3,150
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf)	(1.46)
2018 | Liquids Swaps | Natural Gas Liquids
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMGal and Bcf) | gal	34.0
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf) | $ / gal	0.61
2018 | Basin Specific Swaps - West Texas/Waha | Natural Gas
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMGal and Bcf) | Bcf	1.8
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf) | $ / Mcf	1.70
2018 | Basin Specific Swaps - Permian | Natural Gas
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMGal and Bcf) | Bcf	0.9
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf) | $ / Mcf	2.56
2019 | NYMEX Swaps | Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMGal and Bcf) | mbbl	8,280
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf)	61.66
2019 | NYMEX Three-Way Collars | Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMGal and Bcf) | mbbl	5,760
2019 | Ceiling sold price (call) | Oil | Short
Derivatives, Fair Value [Line Items]
Ceiling sold price (call) (in dollars per Bbl)	61.65
2019 | Floor Purchased and Sold Price (Put) | Oil | Short
Derivatives, Fair Value [Line Items]
Floor purchased and sold price (in dollars per Bbl)	35.94
2019 | Floor Purchased and Sold Price (Put) | Oil | Long
Derivatives, Fair Value [Line Items]
Floor purchased and sold price (in dollars per Bbl)	45.94
2019 | WTI/WTI Basis Swaps | Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMGal and Bcf) | mbbl	16,560
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf)	(5.52)
2019 | Liquids Swaps | Natural Gas Liquids
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMGal and Bcf) | gal	115.9
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf) | $ / gal	0.65
2020 | WTI/WTI Basis Swaps | Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMGal and Bcf) | mbbl	15,120
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf)	(1.20)