Fair Value Measurements - Level 3 Measurements of Derivative Commodity Instruments (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2015 USD ($) $ / Mcf $ / bbl	Dec. 31, 2014 USD ($)
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities | $	$ (14,105)	$ (988)
Derivative assets | $	147,789	$ 322,337
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTS/WTI | 2015
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities | $	$ (5,427)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTS/WTI | 2015 | Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel	0.59
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTS/WTI | 2015 | Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel	0.76
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTS/WTI | 2016
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities | $	$ (2,676)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTS/WTI | 2016 | Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel	(0.26)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTS/WTI | 2016 | Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel	(0.80)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2015
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities | $	$ (16,604)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2015 | Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel	(0.05)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2015 | Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel	(0.35)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2016
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities | $	$ (7,866)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2016 | Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel	(0.80)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2016 | Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel	(0.88)
Discounted Cash Flow Valuation Technique | Level 3 | Natural Gas Basis - San Juan | 2015
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative assets | $	$ 14,336
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 | $	$ 4,174
Price per cubic foot | $ / Mcf	(0.10)