Derivative Activities - Derivative Volumes Hedged and Average Hedge Prices (Detail)	Dec. 31, 2012 bbl
Collars [Member] | Crude Oil 2013 [Member]
Derivative [Line Items]
Volume Hedged	3,000
Average floor price	90.60
Average cap price	100.00
Collars [Member] | Crude Oil 2014 [Member]
Derivative [Line Items]
Volume Hedged	2,000
Average floor price	85.55
Average cap price	100.00
Collars [Member] | Natural Gas 2013 [Member]
Derivative [Line Items]
Volume Hedged	280,000
Average floor price	4.59
Average cap price	5.05
Collars [Member] | Natural Gas 2014 [Member]
Derivative [Line Items]
Volume Hedged	385,000
Average floor price	3.80
Average cap price	4.48
Swaps [Member] | Crude Oil 2013 [Member]
Derivative [Line Items]
Volume Hedged	5,081
Average hedge price	96.59
Swaps [Member] | Crude Oil 2014 [Member]
Derivative [Line Items]
Volume Hedged	4,000
Average hedge price	94.56
Swaps [Member] | NGLs Propane 2013 [Member]
Derivative [Line Items]
Volume Hedged	5,000
Average hedge price	35.55
Swaps [Member] | Natural Gas 2013 [Member]
Derivative [Line Items]
Volume Hedged	213,384
Average hedge price	3.64
Sold swaps [Member] | NGLs Natural Gasoline 2013 [Member]
Derivative [Line Items]
Volume Hedged	8,000
Average hedge price	89.64
Re-purchased swaps [Member] | NGLs Natural Gasoline 2013 [Member]
Derivative [Line Items]
Volume Hedged	1,500
Average hedge price	76.30