Derivative Commodity Instruments - Derivative Transactions (Details) gal in Millions	3 Months Ended
	Mar. 31, 2018 MBbls gal Bcf $ / bbl $ / Mcf $ / gal
2018 | NYMEX Swaps | Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMgal and Bcf) | MBbls	1,380
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf)	60.24
2018 | NYMEX Three-Way Collars | Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMgal and Bcf) | MBbls	10,125
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 price (in dollars per Bbl)	35.47
2018 | Floor Purchased and Sold Price (Put) | Oil | Long
Derivatives, Fair Value [Line Items]
Floor 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) | MBbls	8,370
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf)	(1.03)
2018 | Liquids Swaps | Natural Gas Liquids
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMgal and Bcf) | gal	102.1
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	5.4
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	2.7
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) | MBbls	2,880
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf)	56.52
2019 | NYMEX Three-Way Collars | Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMgal and Bcf) | MBbls	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 price (in dollars per Bbl)	35.94
2019 | Floor Purchased and Sold Price (Put) | Oil | Long
Derivatives, Fair Value [Line Items]
Floor 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) | MBbls	6,120
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf)	(0.75)
2019 | Liquids Swaps | Natural Gas Liquids
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, MMgal and Bcf) | gal	85.7
Weighted Average Contract Price (in dollars per Bbl, Gal and Mcf) | $ / gal	0.64