Derivative Instruments (Details 3) (Crude Oil)	Mar. 31, 2013
April 2013-December 2013 Term | NYMEX WTI to Midland | Crude Oil Sales - Basis Swap - Derivative 3
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	4,000
Derivative, Swap Type, Average Fixed Price	1.48
Full 2014 Term | NYMEX WTI | Crude Oil Sales - Swap - Derivative 1
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	11,500
Derivative, Swap Type, Average Fixed Price	90.14
Full 2014 Term | NYMEX WTI to ICE Brent | Crude Oil Sales - Basis Swap - Derivative 1
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	10,000
Derivative, Swap Type, Average Fixed Price	11.60
Full 2015 Term | NYMEX WTI to ICE Brent | Crude Oil Sales - Basis Swap - Derivative 2
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	8,000
Derivative, Swap Type, Average Fixed Price	11.60