Derivative Instruments (Details)	Mar. 31, 2014 mmbls
2014 | Oil derivative instruments | Swap
Derivative
Hedged volume (MBbls)	3,713
Average price ($/Bbl)	91.26
2014 | Oil derivative instruments | Crude Oil Sales - Collars
Derivative
Hedged volume (MBbls)	550
Derivative, floor price ($/Bbl)	90.00
Derivative, cap price ($/Bbl)	102.87
2014 | Oil derivative instruments | Crude Oil Sales - Three-way collars - Derivative 1
Derivative
Hedged volume (MBbls)	2,338
2014 | Oil derivative instruments | Crude Oil Sales - Three-way collars - Derivative 2
Derivative
Hedged volume (MBbls)	275
2014 | Oil derivative instruments | Short | Crude Oil Sales - Three-way collars - Derivative 1
Derivative
Derivative, floor price ($/Bbl)	72.11
Derivative, cap price ($/Bbl)	109.79
2014 | Oil derivative instruments | Short | Crude Oil Sales - Three-way collars - Derivative 2
Derivative
Derivative, floor price ($/Bbl)	80.00
Derivative, cap price ($/Bbl)	114.05
2014 | Oil derivative instruments | Long | Crude Oil Sales - Three-way collars - Derivative 1
Derivative
Derivative, floor price ($/Bbl)	93.76
2014 | Oil derivative instruments | Long | Crude Oil Sales - Three-way collars - Derivative 2
Derivative
Derivative, floor price ($/Bbl)	100.00
2014 | Oil basis differential commodity contract | ICE Brent - NYMEX WTI basis swaps
Derivative
Hedged volume (MBbls)	2,750
Hedged differential ($/Bbl)	11.60
2014 | Oil timing differential positions | Trade month roll swaps
Derivative
Hedged volume (MBbls)	1,375	[1]
Hedged differential ($/Bbl)	0.32	[1]
2015 | Oil derivative instruments | Swap
Derivative
Hedged volume (MBbls)	0
Average price ($/Bbl)	0
2015 | Oil derivative instruments | Crude Oil Sales - Collars
Derivative
Hedged volume (MBbls)	0
Derivative, floor price ($/Bbl)	0
Derivative, cap price ($/Bbl)	0
2015 | Oil derivative instruments | Crude Oil Sales - Three-way collars - Derivative 1
Derivative
Hedged volume (MBbls)	1,095
2015 | Oil derivative instruments | Crude Oil Sales - Three-way collars - Derivative 2
Derivative
Hedged volume (MBbls)	0
2015 | Oil derivative instruments | Short | Crude Oil Sales - Three-way collars - Derivative 1
Derivative
Derivative, floor price ($/Bbl)	70.00
Derivative, cap price ($/Bbl)	101.62
2015 | Oil derivative instruments | Short | Crude Oil Sales - Three-way collars - Derivative 2
Derivative
Derivative, floor price ($/Bbl)	0.00
Derivative, cap price ($/Bbl)	0.00
2015 | Oil derivative instruments | Long | Crude Oil Sales - Three-way collars - Derivative 1
Derivative
Derivative, floor price ($/Bbl)	90.00
2015 | Oil derivative instruments | Long | Crude Oil Sales - Three-way collars - Derivative 2
Derivative
Derivative, floor price ($/Bbl)	0.00
2015 | Oil basis differential commodity contract | ICE Brent - NYMEX WTI basis swaps
Derivative
Hedged volume (MBbls)	2,920
Hedged differential ($/Bbl)	11.60
2015 | Oil timing differential positions | Trade month roll swaps
Derivative
Hedged volume (MBbls)	0	[1]
Hedged differential ($/Bbl)	0.00	[1]

[1] (1) The Company hedges the timing risk associated with the sales price of oil in the Permian Basin. In this operating area, the Company generally sells oil for the delivery month at a sales price based on the average NYMEX WTI price during that month, plus an adjustment calculated as a spread between the weighted average prices of the delivery month, the next month and the following month during the period when the delivery month is prompt (the “trade month roll”).