Derivative Commodity Instruments - Quantitative Disclosures About Fair Value (Details) (Income Approach Valuation Technique [Member], Level 3, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
Natural Gas Basis - San Juan [Member] | 2012
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value as of March 31, 2012	$ 47,977
Natural Gas Basis - San Juan [Member] | 2012 | Minimum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Cubic Foot	0.16
Natural Gas Basis - San Juan [Member] | 2012 | Maximum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Cubic Foot	0.17
Natural Gas Basis - San Juan [Member] | 2013
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value as of March 31, 2012	40,323
Natural Gas Basis - San Juan [Member] | 2013 | Minimum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Cubic Foot	0.19
Natural Gas Basis - San Juan [Member] | 2013 | Maximum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Cubic Foot	0.21
Natural Gas Basis - San Juan [Member] | 2014
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value as of March 31, 2012	23,314
Natural Gas Basis - San Juan [Member] | 2014 | Minimum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Cubic Foot	0.19
Natural Gas Basis - San Juan [Member] | 2014 | Maximum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Cubic Foot	0.21
Oil Basis - WTS/WTI [Member] | 2012
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value as of March 31, 2012	493
Oil Basis - WTS/WTI [Member] | 2012 | Minimum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Barrel	3.17
Oil Basis - WTS/WTI [Member] | 2012 | Maximum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Barrel	3.25
Oil Basis - WTS/WTI [Member] | 2013
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value as of March 31, 2012	(2,392)
Oil Basis - WTS/WTI [Member] | 2013 | Minimum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Barrel	2.5
Oil Basis - WTS/WTI [Member] | 2013 | Maximum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Barrel	2.85
Natural Gas Liquids [Member] | 2012
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value as of March 31, 2012	(5,339)
Natural Gas Liquids [Member] | 2012 | Minimum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Gallon	1.0
Natural Gas Liquids [Member] | 2012 | Maximum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Gallon	1.18
Natural Gas Liquids [Member] | 2013
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value as of March 31, 2012	$ 547
Natural Gas Liquids [Member] | 2013 | Minimum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Gallon	0.96
Natural Gas Liquids [Member] | 2013 | Maximum [Member]
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Fair Value Inputs, Price Per Gallon	1.05