Commodity Derivative Positions (Detail) (Commodity contracts, USD $)	12 Months Ended
	Dec. 31, 2011 MMBtu
Premiums - Deferred
Derivative Instruments Related to Oil and Gas Production [Line Items]
Fair Value Liability	$ 3,570,000	[1]
Settlements to be paid in subsequent period
Derivative Instruments Related to Oil and Gas Production [Line Items]
Fair Value Asset	162,000
Natural Gas | Group Three
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	First quarter 2012
Average Volume Per Day	20,000.00
Weighted Average Price Floor/Swap	6.00
Weighted Average Price Ceiling	8.50
Fair Value Asset	5,394,000
Instrument Type	Collars
Natural Gas | Group Four
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	First quarter 2012
Average Volume Per Day	10,000.00
Weighted Average Price Floor/Swap	5.10
Fair Value Asset	1,880,000
Instrument Type	Swaps
Natural Gas | Group Five
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second quarter 2012
Average Volume Per Day	20,000.00
Weighted Average Price Floor/Swap	5.31
Fair Value Asset	3,935,000
Instrument Type	Swaps
Natural Gas | Group Six
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third quarter 2012
Average Volume Per Day	20,000.00
Weighted Average Price Floor/Swap	5.31
Fair Value Asset	3,706,000
Instrument Type	Swaps
Natural Gas | Group Seven
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth quarter 2012
Average Volume Per Day	10,000.00
Weighted Average Price Floor/Swap	5.10
Fair Value Asset	1,424,000
Instrument Type	Swaps
Crude Oil | Group Eight
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	First quarter 2012
Average Volume Per Day	1.00
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	97.00
Fair Value Liability	361,000
Instrument Type	Collars
Crude Oil | Group Nine
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second quarter 2012
Average Volume Per Day	1.00
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	97.00
Fair Value Liability	447,000
Instrument Type	Collars
Crude Oil | Group Ten
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third quarter 2012
Average Volume Per Day	1.00
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	97.00
Fair Value Liability	412,000
Instrument Type	Collars
Crude Oil | Group Eleven
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth quarter 2012
Average Volume Per Day	1.00
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	97.00
Fair Value Liability	350,000
Instrument Type	Collars
Crude Oil | Group Twelve
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	First quarter 2013
Average Volume Per Day	1.00
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	100.00
Fair Value Liability	146,000
Instrument Type	Collars
Crude Oil | Group Thirteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second quarter 2013
Average Volume Per Day	1.00
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	100.00
Fair Value Liability	80,000
Instrument Type	Collars
Crude Oil | Group Fourteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third quarter 2013
Average Volume Per Day	1.00
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	100.00
Fair Value Liability	14,000
Instrument Type	Collars
Crude Oil | Group Fifteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth quarter 2013
Average Volume Per Day	1.00
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	100.00
Fair Value Asset	29,000
Instrument Type	Collars
Crude Oil | Group Sixteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	First quarter 2012
Average Volume Per Day	1.40
Weighted Average Price Floor/Swap	101.16
Fair Value Asset	261,000
Instrument Type	Swaps
Crude Oil | Group Seventeen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second quarter 2012
Average Volume Per Day	1.00
Weighted Average Price Floor/Swap	100.61
Fair Value Asset	106,000
Instrument Type	Swaps
Crude Oil | Group Eighteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third quarter 2012
Average Volume Per Day	0.50
Weighted Average Price Floor/Swap	100.00
Fair Value Asset	52,000
Instrument Type	Swaps
Crude Oil | Group Nineteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth quarter 2012
Average Volume Per Day	0.50
Weighted Average Price Floor/Swap	100.00
Fair Value Asset	88,000
Instrument Type	Swaps
Crude Oil | Group Twenty
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	First quarter 2013
Average Volume Per Day	1.10
Weighted Average Price Floor/Swap	100.00
Fair Value Liability	1,049,000
Instrument Type	Swaption
Crude Oil | Group Twenty One
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second quarter 2013
Average Volume Per Day	1.00
Weighted Average Price Floor/Swap	100.00
Fair Value Liability	849,000
Instrument Type	Swaption
Crude Oil | Group Twenty Two
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third quarter 2013
Average Volume Per Day	0.90
Weighted Average Price Floor/Swap	100.00
Fair Value Liability	674,000
Instrument Type	Swaption
Crude Oil | Group Twenty Three
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth quarter 2013
Average Volume Per Day	0.75
Weighted Average Price Floor/Swap	100.00
Fair Value Liability	$ 497,000
Instrument Type	Swaption

[1] Premiums are attributable to the crude oil collars for 2013 and are included in noncurrent derivative liabilities.