Commodity Derivative Positions (Detail) $ in Thousands	6 Months Ended
Jun. 30, 2018 USD ($) bbl $ / bbl
Settlement Agreement [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Fair Value Asset
Fair Value Liability	$ 4,607
Crude Oil \| Third Quarter 2018 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	10,455
Derivative, Swap Type, Average Fixed Price \| $ / bbl	57.05
Fair Value Asset	$ 0
Fair Value Liability	$ 14,270
Crude Oil \| Fourth Quarter 2018 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	10,455
Derivative, Swap Type, Average Fixed Price \| $ / bbl	57.05
Fair Value Asset	$ 0
Fair Value Liability	$ 11,332
Crude Oil \| First Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	6,446
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.46
Fair Value Asset	$ 0
Fair Value Liability	$ 6,999
Crude Oil \| Second Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	6,421
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.48
Fair Value Asset	$ 0
Fair Value Liability	$ 6,115
Crude Oil \| Third Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	6,397
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.50
Fair Value Asset	$ 0
Fair Value Liability	$ 5,337
Crude Oil \| Fourth Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	6,398
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.50
Fair Value Asset	$ 0
Fair Value Liability	$ 4,635
Crude Oil \| First Quarter 2020 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	6,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.09
Fair Value Asset	$ 0
Fair Value Liability	$ 3,846
Crude Oil \| Second Quarter 2020 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	6,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.09
Fair Value Asset	$ 0
Fair Value Liability	$ 3,302
Crude Oil \| Third Quarter 2020 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	6,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.09
Fair Value Asset	$ 0
Fair Value Liability	$ 2,844
Crude Oil \| Fourth Quarter 2020 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	6,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.09
Fair Value Asset	$ 0
Fair Value Liability	$ 2,451
Louisiana Light Sweet [Member] \| Third Quarter 2018 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps-LLS
Notional Volume, per day \| bbl	6,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	65.27
Fair Value Asset	$ 0
Fair Value Liability	$ 5,605
Louisiana Light Sweet [Member] \| Fourth Quarter 2018 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps-LLS
Notional Volume, per day \| bbl	6,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	65.27
Fair Value Asset	$ 0
Fair Value Liability	$ 4,418
Louisiana Light Sweet [Member] \| First Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps-LLS
Notional Volume, per day \| bbl	5,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	59.17
Fair Value Asset	$ 0
Fair Value Liability	$ 5,310
Louisiana Light Sweet [Member] \| Second Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps-LLS
Notional Volume, per day \| bbl	5,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	59.17
Fair Value Asset	$ 0
Fair Value Liability	$ 4,568
Louisiana Light Sweet [Member] \| Third Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps-LLS
Notional Volume, per day \| bbl	5,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	59.17
Fair Value Asset	$ 0
Fair Value Liability	$ 3,876
Louisiana Light Sweet [Member] \| Fourth Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps-LLS
Notional Volume, per day \| bbl	5,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	59.17
Fair Value Asset	$ 0
Fair Value Liability	$ 3,221

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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Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as an asset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(2)
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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(n)(2))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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