Hedging Positions (Detail) (Subsequent Event [Member], USD $)	Nov. 02, 2012
2012 Hedging Position One | Natural Gas
Derivative [Line Items]
Daily Volume	$ 10,000
Swap Price	5.035
2012 Hedging Position One | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	90.300
2012 Hedging Position Two | Natural Gas
Derivative [Line Items]
Daily Volume	10,000
Swap Price	5.040
2012 Hedging Position Two | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	90.410
2012 Hedging Position Three | Natural Gas
Derivative [Line Items]
Daily Volume	10,000
Swap Price	5.050
2012 Hedging Position Three | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	90.450
2012 Hedging Position Four | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	95.50
2012 Hedging Position Five | Oil
Derivative [Line Items]
Daily Volume	2,000
Swap Price	97.60
2012 Hedging Position Six | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	98.15
2012 Hedging Position Seven | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	100.00
2012 Hedging Position Eight | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	101.55
2012 Hedging Position Nine | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	104.25
2012 Hedging Position Ten | Oil
Derivative [Line Items]
Daily Volume	1,000	[1]
Swap Price	111.02
2013 Hedging Position One | Natural Gas
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.000
2013 Hedging Position One | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	92.800
2013 Hedging Position Two | Natural Gas
Derivative [Line Items]
Daily Volume	10,000
Swap Price	5.270
2013 Hedging Position Two | Oil
Derivative [Line Items]
Daily Volume	2,000
Swap Price	94.050
2013 Hedging Position Three | Natural Gas
Derivative [Line Items]
Daily Volume	10,000
Swap Price	5.320
2013 Hedging Position Three | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	94.450
2013 Hedging Position Four | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	94.60
2013 Hedging Position Five | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	97.15
2013 Hedging Position Six | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	101.53
2013 Hedging Position Seven | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	103.00
2013 Hedging Position Eight | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	103.15
2013 Hedging Position Nine | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	104.25
2013 Hedging Position Ten | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	104.47
2013 Hedging Position Eleven | Oil
Derivative [Line Items]
Daily Volume	1,000	[1]
Swap Price	104.50
Two Thousand Thirteen Hedging Position Twelve [Member] | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	107.30
2014 Hedging Position One | Natural Gas
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.000
2014 Hedging Position One | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	90.060
2014 Hedging Position Two | Natural Gas
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.250
2014 Hedging Position Two | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	93.550
2014 Hedging Position Three | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	98.00
2014 Hedging Position Four | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	98.30
2014 Hedging Position Five | Oil
Derivative [Line Items]
Daily Volume	1,000
Swap Price	99.65
Two Thousand Fourteen Hedging Position Six [Member] | Oil
Derivative [Line Items]
Daily Volume	1,000	[1]
Swap Price	103.30
2015 Hedging Position One | Natural Gas
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.005
2015 Hedging Position One | Oil
Derivative [Line Items]
Daily Volume	$ 1,000
Swap Price	90.000

[1] Brent oil contract