Fair Value Measurements - Level 3 Measurements of Derivative Commodity Instruments (Details) $ in Thousands	Sep. 30, 2018 USD ($) $ / bbl $ / gal	Dec. 31, 2017 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	$ 4,226	$ 0
Derivative liabilities	(230,229)	$ (80,265)
Oil Basis - WTI/WTI | 2018 | Discounted Cash Flow Valuation Technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	$ 24,790
Oil Basis - WTI/WTI | 2018 | Minimum | Discounted Cash Flow Valuation Technique | Level 3 | Measurement Input, Commodity Forward Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Price per barrel (in dollars per Bbl) | $ / bbl	(9.50)
Oil Basis - WTI/WTI | 2018 | Maximum | Discounted Cash Flow Valuation Technique | Level 3 | Measurement Input, Commodity Forward Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Price per barrel (in dollars per Bbl) | $ / bbl	(9.23)
Oil Basis - WTI/WTI | 2019 | Discounted Cash Flow Valuation Technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	$ 7,417
Oil Basis - WTI/WTI | 2019 | Minimum | Discounted Cash Flow Valuation Technique | Level 3 | Measurement Input, Commodity Forward Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Price per barrel (in dollars per Bbl) | $ / bbl	(6.76)
Oil Basis - WTI/WTI | 2019 | Maximum | Discounted Cash Flow Valuation Technique | Level 3 | Measurement Input, Commodity Forward Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Price per barrel (in dollars per Bbl) | $ / bbl	(5.83)
Oil Basis - WTI/WTI | 2020 | Discounted Cash Flow Valuation Technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	$ (11,350)
Oil Basis - WTI/WTI | 2020 | Minimum | Discounted Cash Flow Valuation Technique | Level 3 | Measurement Input, Commodity Forward Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Price per barrel (in dollars per Bbl) | $ / bbl	(0.53)
Oil Basis - WTI/WTI | 2020 | Maximum | Discounted Cash Flow Valuation Technique | Level 3 | Measurement Input, Commodity Forward Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Price per barrel (in dollars per Bbl) | $ / bbl	(0.26)
Natural Gas Liquids | 2018 | Discounted Cash Flow Valuation Technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liabilities	$ (17,870)
Natural Gas Liquids | 2018 | Minimum | Discounted Cash Flow Valuation Technique | Level 3 | Measurement Input, Commodity Forward Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Price per gallon (in dollars per gal) | $ / gal	(1.00)
Natural Gas Liquids | 2018 | Maximum | Discounted Cash Flow Valuation Technique | Level 3 | Measurement Input, Commodity Forward Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Price per gallon (in dollars per gal) | $ / gal	(1.01)
Natural Gas Liquids | 2019 | Discounted Cash Flow Valuation Technique | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liabilities	$ (26,493)
Natural Gas Liquids | 2019 | Discounted Cash Flow Valuation Technique | Level 3 | Measurement Input, Commodity Forward Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Price per gallon (in dollars per gal) | $ / gal	0.89