Fair Value Measurements - Level 3 Measurements of Derivative Commodity Instruments (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($) $ / Mcf $ / bbl	Dec. 31, 2014 USD ($)
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities	$ (6,003)	$ (988)
Derivative assets	156,333	$ 322,337
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2015
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities	$ (9,731)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2015 | Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel | $ / bbl	0.09
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2015 | Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel | $ / bbl	0.23
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2016
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities	$ (13,298)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2016 | Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel | $ / bbl	(0.05)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2016 | Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel | $ / bbl	(0.16)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTS/WTI | 2015
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities	$ (2,762)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTS/WTI | 2015 | Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel | $ / bbl	0.32
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTS/WTI | 2015 | Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel | $ / bbl	0.37
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTS/WTI | 2016
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities	$ (3,427)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTS/WTI | 2016 | Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel | $ / bbl	(0.17)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTS/WTI | 2016 | Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel | $ / bbl	0.19
Discounted Cash Flow Valuation Technique | Level 3 | Natural Gas Basis - San Juan | 2015
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative assets	$ 9,018
Discounted Cash Flow Valuation Technique | Level 3 | Natural Gas Basis - San Juan | 2015 | Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per cubic foot | $ / Mcf	(0.09)
Discounted Cash Flow Valuation Technique | Level 3 | Natural Gas Basis - San Juan | 2015 | Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per cubic foot | $ / Mcf	(0.10)
Discounted Cash Flow Valuation Technique | Level 3 | Natural Gas Basis - Permian | 2015
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative assets	$ 2,568
Price per cubic foot | $ / Mcf	(0.10)