Commodity Derivative Positions (Detail) (Commodity contracts, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012 MMBtu
Settlements to be paid in subsequent period
Derivative Instruments Related to Oil and Gas Production [Line Items]
Fair Value Liability	$ 624
Natural Gas | Group Three
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second quarter 2012
Instrument Type	Swaps
Average Volume Per Day	20,000
Weighted Average Price Floor/Swap	5.31
Fair Value Asset	5,667
Natural Gas | Group Four
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third quarter 2012
Instrument Type	Swaps
Average Volume Per Day	20,000
Weighted Average Price Floor/Swap	5.31
Fair Value Asset	5,234
Natural Gas | Group Five
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth quarter 2012
Instrument Type	Swaps
Average Volume Per Day	10,000
Weighted Average Price Floor/Swap	5.10
Fair Value Asset	2,042
Crude Oil | Group Six
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second quarter 2012
Instrument Type	Collars
Average Volume Per Day	1,000
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	97.00
Fair Value Liability	677
Crude Oil | Group Seven
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third quarter 2012
Instrument Type	Collars
Average Volume Per Day	1,000
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	97.00
Fair Value Liability	842
Crude Oil | Group Eight
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth quarter 2012
Instrument Type	Collars
Average Volume Per Day	1,000
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	97.00
Fair Value Liability	904
Crude Oil | Group Nine
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	First quarter 2013
Instrument Type	Collars
Average Volume Per Day	1,000
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	100.00
Fair Value Liability	710
Crude Oil | Group Ten
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second quarter 2013
Instrument Type	Collars
Average Volume Per Day	1,000
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	100.00
Fair Value Liability	647
Crude Oil | Group Eleven
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third quarter 2013
Instrument Type	Collars
Average Volume Per Day	1,000
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	100.00
Fair Value Liability	573
Crude Oil | Group Twelve
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth quarter 2013
Instrument Type	Collars
Average Volume Per Day	1,000
Weighted Average Price Floor/Swap	90.00
Weighted Average Price Ceiling	100.00
Fair Value Liability	491
Crude Oil | Group Thirteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second quarter 2012
Instrument Type	Swaps
Average Volume Per Day	3,000
Weighted Average Price Floor/Swap	103.05
Fair Value Asset	307
Fair Value Liability	472
Crude Oil | Group Fourteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third quarter 2012
Instrument Type	Swaps
Average Volume Per Day	3,000
Weighted Average Price Floor/Swap	104.40
Fair Value Asset	423
Fair Value Liability	504
Crude Oil | Group Fifteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth quarter 2012
Instrument Type	Swaps
Average Volume Per Day	3,000
Weighted Average Price Floor/Swap	104.40
Fair Value Asset	349
Fair Value Liability	569
Crude Oil | Group Sixteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	First Quarter 2013
Instrument Type	Swaps
Average Volume Per Day	2,250
Weighted Average Price Floor/Swap	103.51
Fair Value Asset	81
Fair Value Liability	381
Crude Oil | Group Seventeen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second Quarter 2013
Instrument Type	Swaps
Average Volume Per Day	2,250
Weighted Average Price Floor/Swap	103.51
Fair Value Asset	123
Fair Value Liability	239
Crude Oil | Group Eighteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third Quarter 2013
Instrument Type	Swaps
Average Volume Per Day	1,500
Weighted Average Price Floor/Swap	102.77
Fair Value Asset	84
Fair Value Liability	118
Crude Oil | Group Nineteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth Quarter 2013
Instrument Type	Swaps
Average Volume Per Day	1,500
Weighted Average Price Floor/Swap	102.77
Fair Value Asset	175
Fair Value Liability	73
Crude Oil | Group Twenty
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	First Quarter 2014
Instrument Type	Swaps
Average Volume Per Day	2,000
Weighted Average Price Floor/Swap	100.44
Fair Value Asset	22
Fair Value Liability	53
Crude Oil | Group Twenty One
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second Quarter 2014
Instrument Type	Swaps
Average Volume Per Day	2,000
Weighted Average Price Floor/Swap	100.44
Fair Value Asset	189
Crude Oil | Group Twenty Two
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third Quarter 2014
Instrument Type	Swaps
Average Volume Per Day	1,500
Weighted Average Price Floor/Swap	100.20
Fair Value Asset	265
Crude Oil | Group Twenty Three
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth Quarter 2014
Instrument Type	Swaps
Average Volume Per Day	1,500
Weighted Average Price Floor/Swap	100.20
Fair Value Asset	378
Crude Oil | Group Twenty Four
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	First quarter 2013
Instrument Type	Swaption
Average Volume Per Day	1,100
Weighted Average Price Floor/Swap	100.00
Fair Value Liability	1,195
Crude Oil | Group Twenty Five
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second quarter 2013
Instrument Type	Swaption
Average Volume Per Day	1,000
Weighted Average Price Floor/Swap	100.00
Fair Value Liability	1,013
Crude Oil | Group Twenty Six
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third quarter 2013
Instrument Type	Swaption
Average Volume Per Day	900
Weighted Average Price Floor/Swap	100.00
Fair Value Liability	831
Crude Oil | Group Twenty Seven
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth quarter 2013
Instrument Type	Swaption
Average Volume Per Day	750
Weighted Average Price Floor/Swap	100.00
Fair Value Liability	620
Crude Oil | Group Twenty Eight
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	First Quarter 2014
Instrument Type	Swaption
Average Volume Per Day	812
Weighted Average Price Floor/Swap	100.00
Fair Value Liability	725
Crude Oil | Group Twenty Nine
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Second Quarter 2014
Instrument Type	Swaption
Average Volume Per Day	812
Weighted Average Price Floor/Swap	100.00
Fair Value Liability	725
Crude Oil | Group Thirty
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Third Quarter 2014
Instrument Type	Swaption
Average Volume Per Day	812
Weighted Average Price Floor/Swap	100.00
Fair Value Liability	725
Crude Oil | Group Thirty One
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Fourth Quarter 2014
Instrument Type	Swaption
Average Volume Per Day	812
Weighted Average Price Floor/Swap	100.00
Fair Value Liability	$ 725