Commodity Derivative Positions (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2013 bbl	Jun. 30, 2013 bbl
Settlements to be paid in subsequent period
Derivative Instruments Related to Oil and Gas Production [Line Items]
Fair Value Asset	$ 292	$ 292
Fair Value Liability	0	0
Crude Oil | Group One
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Collars
Average Volume Per Day (barrels)	500	500
Weighted Average Price, Floor/Swap	90.00	90.00
Weighted Average Price, Ceiling	97.60	97.60
Fair Value Asset	74	74
Fair Value Liability	0	0
Crude Oil | Group Two
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Collars
Average Volume Per Day (barrels)	500	500
Weighted Average Price, Floor/Swap	90.00	90.00
Weighted Average Price, Ceiling	97.60	97.60
Fair Value Asset	131	131
Fair Value Liability	0	0
Crude Oil | Group Four
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term		Jun. 30, 2013
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)	1,900	1,900
Weighted Average Price, Floor/Swap	90.00	90.00
Weighted Average Price, Ceiling	99.17	99.17
Fair Value Asset	0	0
Fair Value Liability	68	68
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)	1,900	1,900
Weighted Average Price, Floor/Swap	90.00	90.00
Weighted Average Price, Ceiling	99.17	99.17
Fair Value Asset	110	110
Fair Value Liability	0	0
Crude Oil | Group Eight
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term		Jun. 30, 2013
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)	6,500	6,500
Weighted Average Price, Floor/Swap	95.61	95.61
Fair Value Asset	1,273	1,273
Fair Value Liability	1,566	1,566
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)	6,500	6,500
Weighted Average Price, Floor/Swap	95.61	95.61
Fair Value Asset	1,720	1,720
Fair Value Liability	837	837
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)	6,000	6,000
Weighted Average Price, Floor/Swap	93.60	93.60
Fair Value Asset	1,494	1,494
Fair Value Liability	682	682
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)	6,000	6,000
Weighted Average Price, Floor/Swap	93.60	93.60
Fair Value Asset	1,778	1,778
Fair Value Liability	142	142
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)	5,500	5,500
Weighted Average Price, Floor/Swap	92.91	92.91
Fair Value Asset	1,862	1,862
Fair Value Liability	0	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)	5,500	5,500
Weighted Average Price, Floor/Swap	92.91	92.91
Fair Value Asset	2,433	2,433
Fair Value Liability	0	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	812
Weighted Average Price, Floor/Swap	100.00	100.00
Fair Value Asset	0	0
Fair Value Liability	88	88
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	812
Weighted Average Price, Floor/Swap	100.00	100.00
Fair Value Asset	0	0
Fair Value Liability	88	88
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	812
Weighted Average Price, Floor/Swap	100.00	100.00
Fair Value Asset	0	0
Fair Value Liability	88	88
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	812
Weighted Average Price, Floor/Swap	100.00	100.00
Fair Value Asset	0	0
Fair Value Liability	88	88
Natural Gas
Derivative Instruments Related to Oil and Gas Production [Line Items]
Fair Value Liability	0	0
Natural Gas | Group Three
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Average Volume Per Day (MMBtu)	5,000	5,000
Weighted Average Price, Floor/Swap	4.50	4.50
Fair Value Asset	211	211
Natural Gas | Group Twenty
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term		Jun. 30, 2013
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	10,000
Weighted Average Price, Floor/Swap	3.50	3.50
Weighted Average Price, Ceiling	4.30	4.30
Fair Value Asset	69	69
Fair Value Liability	0	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	15,000
Weighted Average Price, Floor/Swap	3.67	3.67
Weighted Average Price, Ceiling	4.37	4.37
Fair Value Asset	277	277
Fair Value Liability	0	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	5,000
Weighted Average Price, Floor/Swap	4.00	4.00
Weighted Average Price, Ceiling	4.50	4.50
Fair Value Asset	113	113
Fair Value Liability	0	0
Natural Gas | Group Twenty-Five
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term		Jun. 30, 2013
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)	15,000	15,000
Weighted Average Price, Floor/Swap	3.92	3.92
Fair Value Asset	426	426
Fair Value Liability	0	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)	10,000	10,000
Weighted Average Price, Floor/Swap	4.04	4.04
Fair Value Asset	335	335
Fair Value Liability	0	0
Natural Gas | Group Twenty-Eight
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term		Mar. 31, 2014
Instrument	Swaps
Average Volume Per Day (MMBtu)	10,000	10,000
Weighted Average Price, Floor/Swap	4.28	4.28
Fair Value Asset	346	346
Fair Value Liability	0	0
Natural Gas | Group Twenty-Nine
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term		Jun. 30, 2014
Instrument	Swaps
Average Volume Per Day (MMBtu)	15,000	15,000
Weighted Average Price, Floor/Swap	4.10	4.10
Fair Value Asset	388	388
Fair Value Liability	0	0
Natural Gas | Group Thirty
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term		Sep. 30, 2014
Instrument	Swaps
Average Volume Per Day (MMBtu)	15,000	15,000
Weighted Average Price, Floor/Swap	4.10	4.10
Fair Value Asset	285	285
Fair Value Liability	0	0
Natural Gas | Group Thirty-One
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Average Volume Per Day (MMBtu)	5,000	5,000
Weighted Average Price, Floor/Swap	4.50	4.50
Fair Value Asset	119	119
Fair Value Liability	$ 0	$ 0