Commodity Derivative Positions (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 bbl
Settlements to be paid in subsequent period
Derivative Instruments Related to Oil and Gas Production [Line Items]
Fair Value Asset	$ 1,557
Fair Value Liability	0
Crude Oil
Derivative Instruments Related to Oil and Gas Production [Line Items]
Weighted Average Price, Ceiling	100.00
Crude Oil | Group Three
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Mar. 31, 2013
Instrument	Collars
Average Volume Per Day (barrels)	1,000
Weighted Average Price, Floor/Swap	90.00
Weighted Average Price, Ceiling	100.00
Fair Value Asset	119
Fair Value Liability	0
Crude Oil | Group Four
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Jun. 30, 2013
Instrument	Collars
Average Volume Per Day (barrels)	1,000
Weighted Average Price, Floor/Swap	90.00
Fair Value Asset	124
Fair Value Liability	0
Crude Oil | Group Five
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Sep. 30, 2013
Instrument	Collars
Average Volume Per Day (barrels)	1,000
Weighted Average Price, Floor/Swap	90.00
Fair Value Asset	123
Fair Value Liability	0
Crude Oil | Group Six
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2013
Instrument	Collars
Average Volume Per Day (barrels)	1,000
Weighted Average Price, Floor/Swap	90.00
Fair Value Asset	151
Fair Value Liability	0
Crude Oil | Group Seven
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Mar. 31, 2013
Instrument	Swaps
Average Volume Per Day (barrels)	2,250
Weighted Average Price, Floor/Swap	103.51
Fair Value Asset	2,244
Fair Value Liability	0
Crude Oil | Group Eight
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Jun. 30, 2013
Instrument	Swaps
Average Volume Per Day (barrels)	2,250
Weighted Average Price, Floor/Swap	103.51
Fair Value Asset	2,040
Fair Value Liability	0
Crude Oil | Group Nine
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Sep. 30, 2013
Instrument	Swaps
Average Volume Per Day (barrels)	1,500
Weighted Average Price, Floor/Swap	102.77
Fair Value Asset	1,248
Fair Value Liability	0
Crude Oil | Group Ten
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2013
Instrument	Swaps
Average Volume Per Day (barrels)	1,500
Weighted Average Price, Floor/Swap	102.77
Fair Value Asset	1,296
Fair Value Liability	0
Crude Oil | Group Eleven
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Mar. 31, 2014
Instrument	Swaps
Average Volume Per Day (barrels)	2,000
Weighted Average Price, Floor/Swap	100.44
Fair Value Asset	1,360
Fair Value Liability	0
Crude Oil | Group Twelve
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Jun. 30, 2014
Instrument	Swaps
Average Volume Per Day (barrels)	2,000
Weighted Average Price, Floor/Swap	100.44
Fair Value Asset	1,446
Fair Value Liability	0
Crude Oil | Group Thirteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Sep. 30, 2014
Instrument	Swaps
Average Volume Per Day (barrels)	1,500
Weighted Average Price, Floor/Swap	100.20
Fair Value Asset	1,128
Fair Value Liability	0
Crude Oil | Group Fourteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2014
Instrument	Swaps
Average Volume Per Day (barrels)	1,500
Weighted Average Price, Floor/Swap	100.20
Fair Value Asset	1,179
Fair Value Liability	0
Crude Oil | Group Fifteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Mar. 31, 2014
Instrument	Swaption
Average Volume Per Day (barrels)	812
Weighted Average Price, Floor/Swap	100.00
Fair Value Asset	0
Fair Value Liability	356
Crude Oil | Group Sixteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Jun. 30, 2014
Instrument	Swaption
Average Volume Per Day (barrels)	812
Weighted Average Price, Floor/Swap	100.00
Fair Value Asset	0
Fair Value Liability	355
Crude Oil | Group Seventeen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Sep. 30, 2014
Instrument	Swaption
Average Volume Per Day (barrels)	812
Weighted Average Price, Floor/Swap	100.00
Fair Value Asset	0
Fair Value Liability	355
Crude Oil | Group Eighteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2014
Instrument	Swaption
Average Volume Per Day (barrels)	812
Weighted Average Price, Floor/Swap	100.00
Fair Value Asset	0
Fair Value Liability	355
Natural Gas | Group Nineteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Mar. 31, 2013
Instrument	Collars
Average Volume Per Day (MMBtu)	10,000
Weighted Average Price, Floor/Swap	3.50
Weighted Average Price, Ceiling	4.30
Fair Value Asset	187
Fair Value Liability	0
Natural Gas | Group Twenty
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Jun. 30, 2013
Instrument	Collars
Average Volume Per Day (MMBtu)	10,000
Weighted Average Price, Floor/Swap	3.50
Weighted Average Price, Ceiling	4.30
Fair Value Asset	219
Fair Value Liability	0
Natural Gas | Group Twenty One
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Sep. 30, 2013
Instrument	Collars
Average Volume Per Day (MMBtu)	10,000
Weighted Average Price, Floor/Swap	3.50
Weighted Average Price, Ceiling	4.30
Fair Value Asset	165
Fair Value Liability	0
Natural Gas | Group Twenty Two
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2013
Instrument	Collars
Average Volume Per Day (MMBtu)	15,000
Weighted Average Price, Floor/Swap	3.67
Weighted Average Price, Ceiling	4.37
Fair Value Asset	216
Fair Value Liability	0
Natural Gas | Group Twenty Three
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Mar. 31, 2014
Instrument	Collars
Average Volume Per Day (MMBtu)	5,000
Weighted Average Price, Floor/Swap	4.00
Weighted Average Price, Ceiling	4.50
Fair Value Asset	68
Fair Value Liability	0
Natural Gas | Group Twenty Four
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Mar. 31, 2013
Instrument	Swaps
Average Volume Per Day (MMBtu)	10,000
Weighted Average Price, Floor/Swap	4.01
Fair Value Asset	587
Fair Value Liability	0
Natural Gas | Group Twenty Five
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Jun. 30, 2013
Instrument	Swaps
Average Volume Per Day (MMBtu)	10,000
Weighted Average Price, Floor/Swap	4.01
Fair Value Asset	504
Fair Value Liability	0
Natural Gas | Group Twenty Six
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Sep. 30, 2013
Instrument	Swaps
Average Volume Per Day (MMBtu)	10,000
Weighted Average Price, Floor/Swap	4.01
Fair Value Asset	391
Fair Value Liability	0
Natural Gas | Group Twenty Seven
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2013
Instrument	Swaps
Average Volume Per Day (MMBtu)	5,000
Weighted Average Price, Floor/Swap	4.04
Fair Value Asset	121
Fair Value Liability	$ 0