Commodity Derivative Positions (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 bbl
Settlements to be paid in subsequent period
Derivative Instruments Related to Oil and Gas Production [Line Items]
Fair Value Asset	$ 954
Fair Value Liability	0
Crude Oil
Derivative Instruments Related to Oil and Gas Production [Line Items]
Weighted Average Price, Ceiling	99.17
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)	1,900
Weighted Average Price, Floor/Swap	90.00
Fair Value Asset	0
Fair Value Liability	164
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
Weighted Average Price, Floor/Swap	90.00
Fair Value Asset	0
Fair Value Liability	235
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
Weighted Average Price, Floor/Swap	90.00
Fair Value Asset	0
Fair Value Liability	81
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)	3,750
Weighted Average Price, Floor/Swap	101.26
Fair Value Asset	1,460
Fair Value Liability	173
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)	4,000
Weighted Average Price, Floor/Swap	98.43
Fair Value Asset	1,038
Fair Value Liability	550
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)	4,000
Weighted Average Price, Floor/Swap	98.43
Fair Value Asset	1,355
Fair Value Liability	357
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)	4,000
Weighted Average Price, Floor/Swap	95.27
Fair Value Asset	1,093
Fair Value Liability	720
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)	4,000
Weighted Average Price, Floor/Swap	95.27
Fair Value Asset	1,312
Fair Value Liability	519
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)	3,500
Weighted Average Price, Floor/Swap	94.43
Fair Value Asset	1,096
Fair Value Liability	347
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)	3,500
Weighted Average Price, Floor/Swap	94.43
Fair Value Asset	1,199
Fair Value Liability	210
Crude Oil | Group Fifteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Mar. 31, 2014
Instrument	Swaptions
Average Volume Per Day (barrels)	1,812
Weighted Average Price, Floor/Swap	100.00
Fair Value Asset	0
Fair Value Liability	281
Crude Oil | Group Sixteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Jun. 30, 2014
Instrument	Swaptions
Average Volume Per Day (barrels)	1,812
Weighted Average Price, Floor/Swap	100.00
Fair Value Asset	0
Fair Value Liability	280
Crude Oil | Group Seventeen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Sep. 30, 2014
Instrument	Swaptions
Average Volume Per Day (barrels)	1,812
Weighted Average Price, Floor/Swap	100.00
Fair Value Asset	0
Fair Value Liability	280
Crude Oil | Group Eighteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2014
Instrument	Swaptions
Average Volume Per Day (barrels)	1,812
Weighted Average Price, Floor/Swap	100.00
Fair Value Asset	0
Fair Value Liability	280
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	0
Fair Value Liability	34
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	0
Fair Value Liability	125
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	15
Fair Value Liability	222
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	0
Fair Value Liability	58
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)	15,000
Weighted Average Price, Floor/Swap	3.92
Fair Value Asset	13
Fair Value Liability	151
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
Weighted Average Price, Floor/Swap	3.92
Fair Value Asset	0
Fair Value Liability	271
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
Weighted Average Price, Floor/Swap	4.04
Fair Value Asset	0
Fair Value Liability	160
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)	5,000
Weighted Average Price, Floor/Swap	4.05
Fair Value Asset	0
Fair Value Liability	145
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)	10,000
Weighted Average Price, Floor/Swap	4.03
Fair Value Asset	0
Fair Value Liability	53
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)	10,000
Weighted Average Price, Floor/Swap	4.03
Fair Value Asset	0
Fair Value Liability	$ 105