Risk Management and Derivative Instruments (Details 2) (Not designated as Hedging Instrument, Commodity Derivatives, USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Risk Management and Derivative Instruments
Total	$ (19,233)	$ (4,113)
Derivative assets:
Gross Recognized Assets	17,176	23,601
Gross Amounts Offset, Assets	14,070	16,189
Net Recognized Fair Value Assets	3,106	7,412
Derivative liabilities:
Gross Recognized Liabilities	36,409	27,714
Gross Amounts Offset, Liabilities	14,070	16,189
Net Recognized Fair Value Liabilities	22,339	11,525
Current Assets
Derivative assets:
Gross Recognized Assets	15,893	21,603
Gross Amounts Offset, Assets	13,958	15,908
Net Recognized Fair Value Assets	1,935	5,695
Derivative liabilities:
Gross Recognized Liabilities	27,202	23,490
Gross Amounts Offset, Liabilities	13,958	15,908
Net Recognized Fair Value Liabilities	13,244	7,582
Non-Current Assets
Derivative assets:
Gross Recognized Assets	1,283	1,998
Gross Amounts Offset, Assets	112	281
Net Recognized Fair Value Assets	1,171	1,717
Derivative liabilities:
Gross Recognized Liabilities	9,207	4,224
Gross Amounts Offset, Liabilities	112	281
Net Recognized Fair Value Liabilities	9,095	3,943
Swaps \| Current Assets \| Oil
Derivative assets:
Gross Recognized Assets	11,888	16,004
Swaps \| Current Assets \| NGL
Derivative assets:
Gross Recognized Assets	1,729	1,624
Swaps \| Non-Current Assets \| Oil
Derivative assets:
Gross Recognized Assets	87	129
Swaps \| Non-Current Assets \| NGL
Derivative assets:
Gross Recognized Assets	543	729
Swaps \| Current Liabilities \| Oil
Derivative liabilities:
Gross Recognized Liabilities	18,305	11,485
Swaps \| Current Liabilities \| NGL
Derivative liabilities:
Gross Recognized Liabilities	134	336
Swaps \| Non-Current Liabilities \| Oil
Derivative liabilities:
Gross Recognized Liabilities	8,292	3,606
Swaps \| Non-Current Liabilities \| NGL
Derivative liabilities:
Gross Recognized Liabilities	7	122
Collars \| Current Assets \| Oil
Derivative assets:
Gross Recognized Assets	80	221
Collars \| Current Assets \| Gas
Derivative assets:
Gross Recognized Assets	430	1,129
Collars \| Non-Current Assets \| Oil
Derivative assets:
Gross Recognized Assets	140	207
Collars \| Non-Current Assets \| Gas
Derivative assets:
Gross Recognized Assets	513	897
Collars \| Current Liabilities \| Oil
Derivative liabilities:
Gross Recognized Liabilities	347	238
Collars \| Current Liabilities \| Gas
Derivative liabilities:
Gross Recognized Liabilities	353	112
Collars \| Non-Current Liabilities \| Oil
Derivative liabilities:
Gross Recognized Liabilities	29	49
Collars \| Non-Current Liabilities \| Gas
Derivative liabilities:
Gross Recognized Liabilities	77	73
Basis Differential Swaps \| Current Assets
Derivative assets:
Gross Recognized Assets	1,766	2,625
Basis Differential Swaps \| Non-Current Assets
Derivative assets:
Gross Recognized Assets		36
Basis Differential Swaps \| Current Liabilities
Derivative liabilities:
Gross Recognized Liabilities	8,063	11,319
Basis Differential Swaps \| Non-Current Liabilities
Derivative liabilities:
Gross Recognized Liabilities	$ 802	$ 374

Fair value of liability associated with derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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