Derivative Activities - Derivative Volumes Hedged and Average Hedge Prices (Detail)	Mar. 31, 2013 MMBTU
Collars | Natural Gas 2013
Derivative [Line Items]
Volume Hedged	280,000
Average floor price	4.59
Average cap price	5.05
Collars | Natural Gas 2014
Derivative [Line Items]
Volume Hedged	402,500
Average floor price	3.81
Average cap price	4.47
Collars | Natural Gas 2015
Derivative [Line Items]
Volume Hedged	95,000
Average floor price	4.06
Average cap price	4.48
Collars | Crude Oil 2013
Derivative [Line Items]
Volume Hedged	3,000
Average floor price	90.60
Average cap price	100.00
Collars | Crude Oil 2014
Derivative [Line Items]
Volume Hedged	2,000
Average floor price	85.55
Average cap price	100.00
Swaps | Natural Gas 2013
Derivative [Line Items]
Volume Hedged	256,127
Average hedge price	3.67
Swaps | Natural Gas 2014
Derivative [Line Items]
Volume Hedged	20,000
Average hedge price	4.08
Swaps | Crude Oil 2013
Derivative [Line Items]
Volume Hedged	5,829
Average hedge price	96.73
Swaps | Crude Oil 2014
Derivative [Line Items]
Volume Hedged	6,000
Average hedge price	94.54
Swaps | Crude Oil 2015
Derivative [Line Items]
Volume Hedged	2,000
Average hedge price	90.20
Swaps | NGLs Propane 2013
Derivative [Line Items]
Volume Hedged	7,000
Average hedge price	36.38
Swaps | NGLs Propane 2014
Derivative [Line Items]
Volume Hedged	1,000
Average hedge price	40.32
Sold Swap | NGLs Natural Gasoline 2013
Derivative [Line Items]
Volume Hedged	8,000
Average hedge price	89.64
Re-purchased Swaps | NGLs Natural Gasoline 2013
Derivative [Line Items]
Volume Hedged	1,500
Average hedge price	76.30