Derivative Activities - Derivative Volumes Hedged and Average Hedge Prices (Detail)	Sep. 30, 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	447,500
Average floor price	3.84
Average cap price	4.48
Collars | Natural Gas 2015
Derivative [Line Items]
Volume Hedged	145,000
Average floor price	4.07
Average cap price	4.56
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	293,370
Average hedge price	3.82
Swaps | Natural Gas 2014
Derivative [Line Items]
Volume Hedged	30,000
Average hedge price	4.17
Swaps | Natural Gas 2015
Derivative [Line Items]
Volume Hedged	7,500
Average hedge price	4.16
Swaps | Crude Oil 2013
Derivative [Line Items]
Volume Hedged	6,825
Average hedge price	96.79
Swaps | Crude Oil 2014
Derivative [Line Items]
Volume Hedged	7,000
Average hedge price	94.14
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	11,000
Average hedge price	37.87
Swaps | NGLs Propane 2014
Derivative [Line Items]
Volume Hedged	7,000
Average hedge price	40.38
Swaps | NGLs Butane 2013
Derivative [Line Items]
Volume Hedged	2,000
Average hedge price	55.44
Swaps | NGLs Butane 2014
Derivative [Line Items]
Volume Hedged	2,000
Average hedge price	54.60
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