Hedging Positions (Detail)	Dec. 31, 2013 MMBTU
Natural Gas [Member] | 2014 Hedging Position One [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.000
Natural Gas [Member] | 2014 Hedging Position Two [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.040
Natural Gas [Member] | 2014 Hedging Position Three [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.105
Natural Gas [Member] | 2014 Hedging Position Four [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.190
Natural Gas [Member] | 2014 Hedging Position Five [Member]
Derivative [Line Items]
Daily Volume	10,000	[1]
Swap Price	4.250
Natural Gas [Member] | 2014 Hedging Position Six [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.250
Natural Gas [Member] | 2014 Hedging Position Seven [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.350
Natural Gas [Member] | 2015 Hedging Position One [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.005
Natural Gas [Member] | 2015 Hedging Position Two [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.120
Natural Gas [Member] | 2015 Hedging Position Three [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.150
Natural Gas [Member] | 2015 Hedging Position Four [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.165
Natural Gas [Member] | 2015 Hedging Position Five [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.220
Natural Gas [Member] | 2015 Hedging Position Six [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.255
Natural Gas [Member] | 2016 Hedging Position One [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.110
Natural Gas [Member] | 2016 Hedging Position Two [Member]
Derivative [Line Items]
Daily Volume	10,000
Swap Price	4.120
Oil [Member] | 2014 Hedging Position One [Member]
Derivative [Line Items]
Daily Volume	1
Swap Price	90.060
Oil [Member] | 2014 Hedging Position Two [Member]
Derivative [Line Items]
Daily Volume	1
Swap Price	92.250
Oil [Member] | 2014 Hedging Position Three [Member]
Derivative [Line Items]
Daily Volume	1
Swap Price	93.550
Oil [Member] | 2014 Hedging Position Four [Member]
Derivative [Line Items]
Daily Volume	1
Swap Price	94.000
Oil [Member] | 2014 Hedging Position Five [Member]
Derivative [Line Items]
Daily Volume	1
Swap Price	98.000
Oil [Member] | 2014 Hedging Position Six [Member]
Derivative [Line Items]
Daily Volume	1
Swap Price	98.300
Oil [Member] | 2014 Hedging Position Seven [Member]
Derivative [Line Items]
Daily Volume	2	[2]
Swap Price	98.850
Oil [Member] | 2014 Hedging Position Eight [Member]
Derivative [Line Items]
Daily Volume	1
Swap Price	99.65
Oil [Member] | 2014 Hedging Position Nine [Member]
Derivative [Line Items]
Daily Volume	1	[3]
Swap Price	103.30
Oil [Member] | 2015 Hedging Position One [Member]
Derivative [Line Items]
Daily Volume	1
Swap Price	89.000
Oil [Member] | 2015 Hedging Position Two [Member]
Derivative [Line Items]
Daily Volume	1
Swap Price	90.000

[1] February through December

[2] January through June

[3] Brent crude oil contract