Fair Value Measurements (Level 3 Fair Value Measurements of Derivative Commodity Instruments) (Details) - Crude Oil - 2015 - Level 3 $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) $ / bbl
WTI/WTI Basis Swaps
Fair Value, Option, Quantitative Disclosures [Line Items]
Net derivative asset (liability), at fair value (in USD) | $	$ (13,181)
WTS/WTI Basis Swaps
Fair Value, Option, Quantitative Disclosures [Line Items]
Net derivative asset (liability), at fair value (in USD) | $	$ (2,878)
Discounted Cash Flow Valuation Technique | Minimum | WTI/WTI Basis Swaps
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value inputs, derivative, nonmonetary notional amount (USD per Mcf)	0.07
Discounted Cash Flow Valuation Technique | Minimum | WTS/WTI Basis Swaps
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value inputs, derivative, nonmonetary notional amount (USD per Mcf)	0.19
Discounted Cash Flow Valuation Technique | Maximum | WTI/WTI Basis Swaps
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value inputs, derivative, nonmonetary notional amount (USD per Mcf)	0.28
Discounted Cash Flow Valuation Technique | Maximum | WTS/WTI Basis Swaps
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value inputs, derivative, nonmonetary notional amount (USD per Mcf)	0.31