Derivative Instruments - Schedule of Outstanding Commodity Derivative Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Derivative [Line Items]
Fair value asset (liability)	$ 315,507
2015 Two-way collar [Member]
Derivative [Line Items]
Total notional amount of oil barrels	2,388.5
Average floor price	87.98
Average ceiling price	103.21
Fair value asset (liability)	75,271
2015 Three-way collars [Member]
Derivative [Line Items]
Total notional amount of oil barrels	263.5
Average sub-floor price	70.59
Average floor price	90.59
Average ceiling price	105.25
Fair value asset (liability)	5,270
2015 Swaps [Member]
Derivative [Line Items]
Total notional amount of oil barrels	5,263.5
Average swap price	90.81
Fair value asset (liability)	181,980
2015 Swaps with subfloors [Member]
Derivative [Line Items]
Total notional amount of oil barrels	186.0
Average swap price	92.60
Average sub-floor price	70.00
Fair value asset (liability)	4,204
Two Thousand Fifteen Deferred Premium Puts [Member]
Derivative [Line Items]
Total notional amount of oil barrels	1,086.0
Average floor price	90.00
Weighted average deferred premium	2.55
Fair value asset (liability)	35,434
Two Thousand Sixteen Two Way Collars [Member]
Derivative [Line Items]
Total notional amount of oil barrels	155.0
Average floor price	86.00
Average ceiling price	103.42
Fair value asset (liability)	4,138
Two Thousand Sixteen Swaps [Member]
Derivative [Line Items]
Total notional amount of oil barrels	310.0
Average swap price	90.15
Fair value asset (liability)	$ 9,210

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

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- Definition

DerivativeAverageDeferredPremium

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- Definition

The average strike price of the sold put that establishes the price at which if the market price falls below, the minimum price would be index price plus the difference between the purchased put (floor) and the sold put strike price.

+ References

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- Definition

The average cap rate on a group of price risk derivatives such as caps or collars. A payment or receipt is triggered if the market rate exceeds the cap rate on the contract.

+ References

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- Definition

The average floor rate on a group of price risk derivatives such as floors or collars. A payment or receipt is triggered if the market rate falls below the floor rate on the contract.

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13495-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

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- Definition

Average fixed price related to the group of price risk swap derivatives.

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