Commodity Derivative Positions (Detail) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($) bbl $ / bbl	Dec. 31, 2017 USD ($)
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative Liability	$ 52,928	$ 41,677
Settlement Agreement [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Fair Value Asset
Fair Value Liability	$ 3,037
Crude Oil \| Second Quarter 2018 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	6,484
Derivative, Swap Type, Average Fixed Price \| $ / bbl	51.09
Fair Value Asset	$ 0
Fair Value Liability	$ 7,888
Crude Oil \| Third Quarter 2018 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	6,455
Derivative, Swap Type, Average Fixed Price \| $ / bbl	51.10
Fair Value Asset	$ 0
Fair Value Liability	$ 6,998
Crude Oil \| Fourth Quarter 2018 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	6,455
Derivative, Swap Type, Average Fixed Price \| $ / bbl	51.10
Fair Value Asset	$ 0
Fair Value Liability	$ 5,960
Crude Oil \| First Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	4,946
Derivative, Swap Type, Average Fixed Price \| $ / bbl	52.03
Fair Value Asset	$ 0
Fair Value Liability	$ 3,372
Crude Oil \| Second Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	4,921
Derivative, Swap Type, Average Fixed Price \| $ / bbl	52.04
Fair Value Asset	$ 0
Fair Value Liability	$ 2,861
Crude Oil \| Third Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	4,897
Derivative, Swap Type, Average Fixed Price \| $ / bbl	52.05
Fair Value Asset	$ 0
Fair Value Liability	$ 2,404
Crude Oil \| Fourth Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	4,898
Derivative, Swap Type, Average Fixed Price \| $ / bbl	52.05
Fair Value Asset	$ 0
Fair Value Liability	$ 2,011
Crude Oil \| First Quarter 2020 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	4,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	52.67
Fair Value Asset	$ 0
Fair Value Liability	$ 1,123
Crude Oil \| Second Quarter 2020 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	4,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	52.67
Fair Value Asset	$ 0
Fair Value Liability	$ 866
Crude Oil \| Third Quarter 2020 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	4,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	52.67
Fair Value Asset	$ 0
Fair Value Liability	$ 650
Crude Oil \| Fourth Quarter 2020 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Notional Volume, per day \| bbl	4,000
Derivative, Swap Type, Average Fixed Price \| $ / bbl	52.67
Fair Value Asset	$ 0
Fair Value Liability	$ 461
Louisiana Light Sweet [Member] \| Second Quarter 2018 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps-LLS
Notional Volume, per day \| bbl	2,500
Derivative, Swap Type, Average Fixed Price \| $ / bbl	55.18
Fair Value Asset	$ 0
Fair Value Liability	$ 2,735
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	2,500
Derivative, Swap Type, Average Fixed Price \| $ / bbl	55.18
Fair Value Asset	$ 0
Fair Value Liability	$ 2,404
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	2,500
Derivative, Swap Type, Average Fixed Price \| $ / bbl	55.18
Fair Value Asset	$ 0
Fair Value Liability	$ 2,003
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	2,500
Derivative, Swap Type, Average Fixed Price \| $ / bbl	51.30
Fair Value Asset	$ 0
Fair Value Liability	$ 2,422
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	2,500
Derivative, Swap Type, Average Fixed Price \| $ / bbl	51.30
Fair Value Asset	$ 0
Fair Value Liability	$ 2,144
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	2,500
Derivative, Swap Type, Average Fixed Price \| $ / bbl	51.30
Fair Value Asset	$ 0
Fair Value Liability	$ 1,897
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	2,500
Derivative, Swap Type, Average Fixed Price \| $ / bbl	51.30
Fair Value Asset	$ 0
Fair Value Liability	$ 1,660

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)
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Description of the type of derivative instrument, such as a swap, forward, and option. Excludes the underlying risk of the instrument.

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