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Price per barrel, used as an input to measure fair value.

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Price per cubic foot, used as an input to measure fair value.

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The hypothetical financial impact of a 10 percent adverse change of contract price on the fair value of commodity price contracts as of the balance sheet date.

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No definition available.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Amount of tax expense (benefit), before reclassification adjustments, related to increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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Fair Value Measurements - Level 3 Measurements of Derivative Commodity Instruments (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative assets	$ 272,675,000us-gaap_DerivativeAssets		$ 322,337,000us-gaap_DerivativeAssets
Derivative liabilities	(13,843,000)us-gaap_DerivativeLiabilities		(988,000)us-gaap_DerivativeLiabilities
Level 3
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Sensitivity Analysis of Fair Value of 10 Percent Change in Commodity Prices	4,000,000
Discounted Cash Flow Valuation Technique \| Level 3 \| Oil Basis - WTS/WTI \| 2015
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities	(6,401,000)
Discounted Cash Flow Valuation Technique \| Level 3 \| Oil Basis - WTS/WTI \| 2015 \| Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Barrel	0.33
Discounted Cash Flow Valuation Technique \| Level 3 \| Oil Basis - WTS/WTI \| 2015 \| Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Barrel	0.39
Discounted Cash Flow Valuation Technique \| Level 3 \| Oil Basis - WTS/WTI \| 2016
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities	(410,000)
Fair Value Inputs, Price Per Barrel	1.40
Discounted Cash Flow Valuation Technique \| Level 3 \| Oil Basis - WTI/WTI \| 2015
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities	(21,257,000)
Discounted Cash Flow Valuation Technique \| Level 3 \| Oil Basis - WTI/WTI \| 2015 \| Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Barrel	0.71
Discounted Cash Flow Valuation Technique \| Level 3 \| Oil Basis - WTI/WTI \| 2015 \| Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Barrel	0.91
Discounted Cash Flow Valuation Technique \| Level 3 \| Oil Basis - WTI/WTI \| 2016
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities	(1,162,000)
Discounted Cash Flow Valuation Technique \| Level 3 \| Oil Basis - WTI/WTI \| 2016 \| Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Barrel	1.75
Discounted Cash Flow Valuation Technique \| Level 3 \| Oil Basis - WTI/WTI \| 2016 \| Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Barrel	1.95
Discounted Cash Flow Valuation Technique \| Level 3 \| Natural Gas Basis - San Juan \| 2015
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative assets	24,223,000
Discounted Cash Flow Valuation Technique \| Level 3 \| Natural Gas Basis - San Juan \| 2015 \| Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Cubic Foot	0.23
Discounted Cash Flow Valuation Technique \| Level 3 \| Natural Gas Basis - San Juan \| 2015 \| Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Cubic Foot	0.25
Discounted Cash Flow Valuation Technique \| Level 3 \| Natural Gas Basis - Permian \| 2015
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative assets	7,420,000
Fair Value Inputs, Price Per Cubic Foot	0.24
Commodity contracts
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Gain (Loss) Recognized in other comprehensive income on derivatives	$ 0	$ 1,000