Commodity Derivative Positions (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 bbl
Settlements to be paid in subsequent period
Derivative Instruments Related to Oil and Gas Production [Line Items]
Fair Value Asset	$ 0
Fair Value Liability	1,761
Crude Oil | Group One
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Sep. 30, 2014
Instrument	Collars
Derivative, Nonmonetary Notional Amount	2,000
Weighted Average Price, Floor/Swap	90.00
Weighted Average Price, Ceiling	94,330.00
Fair Value Asset	0
Fair Value Liability	827
Crude Oil | Group Four [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2014
Instrument	Collars
Derivative, Nonmonetary Notional Amount	2,000
Weighted Average Price, Floor/Swap	90.00
Weighted Average Price, Ceiling	94,330.00
Fair Value Asset	0
Fair Value Liability	420
Crude Oil | Group Five [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Mar. 31, 2015
Instrument	Collars
Derivative, Nonmonetary Notional Amount	4,000
Weighted Average Price, Floor/Swap	87.50
Weighted Average Price, Ceiling	94,660.00
Fair Value Asset	0
Fair Value Liability	278
Crude Oil | Group Six [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Jun. 30, 2015
Instrument	Collars
Derivative, Nonmonetary Notional Amount	4,000
Weighted Average Price, Floor/Swap	87.50
Weighted Average Price, Ceiling	94,660.00
Fair Value Asset	276
Fair Value Liability	0
Crude Oil | Group Eight [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Collars
Derivative, Nonmonetary Notional Amount	3,000
Weighted Average Price, Floor/Swap	86.67
Weighted Average Price, Ceiling	94,730.00
Fair Value Asset	507
Fair Value Liability	0
Crude Oil | Group Two
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Jun. 30, 2014
Instrument	Collars
Derivative, Nonmonetary Notional Amount	2,500
Weighted Average Price, Floor/Swap	92.00
Weighted Average Price, Ceiling	99.46
Fair Value Asset	0
Fair Value Liability	740
Crude Oil | Group Six
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2015
Instrument	Collars
Derivative, Nonmonetary Notional Amount	3,000
Weighted Average Price, Floor/Swap	86.67
Weighted Average Price, Ceiling	94,730.00
Fair Value Asset	766
Fair Value Liability	0
Crude Oil | Group Seven
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Mar. 31, 2015
Instrument	Swaps
Derivative, Nonmonetary Notional Amount	7,000
Derivative, Swap Type, Average Fixed Price	90.79
Fair Value Asset	0
Fair Value Liability	1,440
Crude Oil | Group Eight
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Jun. 30, 2014
Instrument	Swaps
Derivative, Nonmonetary Notional Amount	8,500
Derivative, Swap Type, Average Fixed Price	94.00
Fair Value Asset	0
Fair Value Liability	4,984
Crude Oil | Group Nine
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Sep. 30, 2014
Instrument	Swaps
Derivative, Nonmonetary Notional Amount	10,000
Derivative, Swap Type, Average Fixed Price	93.21
Fair Value Asset	342
Fair Value Liability	4,410
Crude Oil | Group Fourteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2014
Instrument	Swaps
Derivative, Nonmonetary Notional Amount	10,000
Derivative, Swap Type, Average Fixed Price	93.21
Fair Value Asset	709
Fair Value Liability	2,417
Crude Oil | Group Ten
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Mar. 31, 2015
Instrument	Swaptions
Derivative, Nonmonetary Notional Amount	1,000
Derivative, Average Price Risk Option Strike Price	88.00
Fair Value Asset	0
Fair Value Liability	535
Crude Oil | Group Eleven
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Jun. 30, 2015
Instrument	Swaptions
Derivative, Nonmonetary Notional Amount	1,000
Derivative, Average Price Risk Option Strike Price	88.00
Fair Value Asset	0
Fair Value Liability	534
Crude Oil | Group Fifteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Sep. 30, 2015
Instrument	Swaptions
Derivative, Nonmonetary Notional Amount	1,000
Derivative, Average Price Risk Option Strike Price	88.00
Fair Value Asset	0
Fair Value Liability	534
Crude Oil | Group Sixteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2015
Instrument	Swaptions
Derivative, Nonmonetary Notional Amount	1,000
Derivative, Average Price Risk Option Strike Price	88.00
Fair Value Asset	0
Fair Value Liability	534
Crude Oil | Group Nineteen
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Jun. 30, 2015
Instrument	Swaps
Derivative, Nonmonetary Notional Amount	7,000
Derivative, Swap Type, Average Fixed Price	90.79
Fair Value Asset	0
Fair Value Liability	447
Crude Oil | Group Twenty Four
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Sep. 30, 2015
Instrument	Swaps
Derivative, Nonmonetary Notional Amount	6,000
Derivative, Swap Type, Average Fixed Price	90.45
Fair Value Asset	150
Fair Value Liability	0
Crude Oil | Group Thirty-Two
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2015
Instrument	Swaps
Derivative, Nonmonetary Notional Amount	6,000
Derivative, Swap Type, Average Fixed Price	90.45
Fair Value Asset	722
Fair Value Liability	0
Natural Gas | Group Three
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Dec. 31, 2014
Instrument	Swaps
Average Volume Per Day (MMBtu)	5,000
Weighted Average Price, Floor/Swap	4.50
Fair Value Asset	0
Fair Value Liability	2
Natural Gas | Group Twenty-Seven
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	4.10
Fair Value Asset	0
Fair Value Liability	474
Natural Gas | Group Twenty-Eight
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Sep. 30, 2014
Instrument	Swaps
Average Volume Per Day (MMBtu)	15,000
Weighted Average Price, Floor/Swap	4.10
Fair Value Asset	0
Fair Value Liability	450
Natural Gas | Group Thirty-One
Derivative Instruments Related to Oil and Gas Production [Line Items]
Term	Mar. 31, 2015
Instrument	Swaps
Average Volume Per Day (MMBtu)	5,000
Weighted Average Price, Floor/Swap	4.50
Fair Value Asset	0
Fair Value Liability	$ 49