Commodity Derivative Positions (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) bbl Entity $ / bbl
Fourth Quarter 2019 [Member] \| Crude Oil
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Nonmonetary Notional Amount \| bbl	6,398
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.50
Fair Value Asset	$ 3,498
Fair Value Liability	$ 0
Derivative, Type of Instrument	Swaps-WTI
Fourth Quarter 2019 [Member] \| Louisiana Light Sweet [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Nonmonetary Notional Amount \| bbl	5,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	59.17
Fair Value Asset	$ 3,015
Fair Value Liability	$ 0
Derivative, Type of Instrument	Swaps-LLS
Fourth Quarter 2020 [Member] \| Crude Oil
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Nonmonetary Notional Amount \| bbl	6,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.09
Fair Value Asset	$ 2,234
Fair Value Liability	$ 0
Derivative, Type of Instrument	Swaps-WTI
Third Quarter 2019 [Member] \| Crude Oil
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Nonmonetary Notional Amount \| bbl	6,397
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.50
Fair Value Asset	$ 3,821
Fair Value Liability	$ 0
Derivative, Type of Instrument	Swaps-WTI
Third Quarter 2019 [Member] \| Louisiana Light Sweet [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Nonmonetary Notional Amount \| bbl	5,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	59.17
Fair Value Asset	$ 3,092
Fair Value Liability	$ 0
Derivative, Type of Instrument	Swaps-LLS
Third Quarter 2020 [Member] \| Crude Oil
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Nonmonetary Notional Amount \| bbl	6,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.09
Fair Value Asset	$ 2,450
Fair Value Liability	$ 0
Derivative, Type of Instrument	Swaps-WTI
Second Quarter 2019 [Member] \| Crude Oil
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Nonmonetary Notional Amount \| bbl	6,421
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.48
Fair Value Asset	$ 4,307
Fair Value Liability	$ 0
Derivative, Type of Instrument	Swaps-WTI
Second Quarter 2019 [Member] \| Louisiana Light Sweet [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Nonmonetary Notional Amount \| bbl	5,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	59.17
Fair Value Asset	$ 3,203
Fair Value Liability	$ 0
Derivative, Type of Instrument	Swaps-LLS
Second Quarter 2020 [Member] \| Crude Oil
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Nonmonetary Notional Amount \| bbl	6,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.09
Fair Value Asset	$ 2,609
Fair Value Liability	$ 0
Derivative, Type of Instrument	Swaps-WTI
First Quarter 2019 [Member] \| Crude Oil
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Nonmonetary Notional Amount \| bbl	6,446
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.46
Fair Value Asset	$ 4,959
Fair Value Liability	$ 0
Derivative, Type of Instrument	Swaps-WTI
First Quarter 2019 [Member] \| Louisiana Light Sweet [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Nonmonetary Notional Amount \| bbl	5,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	59.17
Fair Value Asset	$ 3,684
Fair Value Liability	$ 0
Derivative, Type of Instrument	Swaps-LLS
First Quarter 2020 [Member] \| Crude Oil
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Nonmonetary Notional Amount \| bbl	6,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	54.09
Fair Value Asset	$ 2,807
Fair Value Liability	$ 0
Derivative, Type of Instrument	Swaps-WTI
Commodity contracts
Derivative Instruments Related to Oil and Gas Production [Line Items]
Number Of Derivative Counterparty \| Entity	8
Settlement Agreement [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Fair Value Asset	$ 4,362

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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+ 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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-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

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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