Supplemental Oil and Gas Reserve Information - Unaudited - Additional Information (Detail)	12 Months Ended
Dec. 31, 2018 MBoe $ / bbl $ / MMBTU	Dec. 31, 2017 MBoe $ / bbl $ / MMBTU	Dec. 31, 2016 MBoe $ / bbl $ / MMBTU
Reserve Quantities [Line Items]
Net positive (negative) revisions of previous estimates (MMBoe)	(16,850)	(19,200)	31,136
Percentage of net positive (negative) revisions	(5.00%)	(6.00%)	14.00%
Positive (negative) revisions of previous estimates - proved developed reserves (MMBoe)	(20,200)	(14,200)
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe)		(5,000)
Additions due to extensions and discoveries (Energy)	38,358	51,153	14,876
Estimated extensions and discoveries of reserves associated with new wells (Energy)	9,000	17,900	6,200
Additional proved undeveloped reserves (Energy)	29,400	33,300	6,500
Percentage of reserves produced from wells in certain formations	75.78657%	100.00%	100.00%
Percentage of proved undeveloped reserves	24.00%	100.00%	100.00%
Divested reserves associated with non-operated properties (Energy)	15,926	1,387	7,635
Purchases of reserves in place (Energy)	32,873	671	66,936
Discount rate of future cash flows	10.00%
Unweighted arithmetic average first-day-of-the-month prices for oil, price per Bbl \| $ / bbl	65.66	51.34	42.60
Unweighted arithmetic average first-day-of-the-month prices for natural gas, price per MMBtu \| $ / MMBTU	3.16	2.99	2.47
Revision Due to Performance
Reserve Quantities [Line Items]
Net positive (negative) revisions of previous estimates (MMBoe)	(42,300)	(39,100)	30,400
Positive (negative) revisions of previous estimates - proved developed reserves (MMBoe)	(33,000)	(29,700)
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe)	(9,300)	(9,400)
Revision of Previous Estimate Due to (Mis)Alignment With Development Plan
Reserve Quantities [Line Items]
Net positive (negative) revisions of previous estimates (MMBoe)	(9,400)	(2,100)	(9,500)
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe)	(9,400)	(1,800)
Revisions Due to Addition of Proved Undeveloped Reserves (PUDs)
Reserve Quantities [Line Items]
Net positive (negative) revisions of previous estimates (MMBoe)	14,700
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe)	14,700
Revision of Previous Estimate Due to Realized Prices
Reserve Quantities [Line Items]
Net positive (negative) revisions of previous estimates (MMBoe)	14,400	16,100	(8,200)
Positive (negative) revisions of previous estimates - proved developed reserves (MMBoe)	12,200	14,100
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe)	2,200	2,000
Revision of Previous Estimate Due to Ownership Adjustments
Reserve Quantities [Line Items]
Net positive (negative) revisions of previous estimates (MMBoe)	5,400	2,500	8,200
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe)	5,600	2,600
Revision of Previous Estimate Due to Higher Gas to Oil Ratio
Reserve Quantities [Line Items]
Net positive (negative) revisions of previous estimates (MMBoe)			8,200
Bakken or Three Forks Formations Area
Reserve Quantities [Line Items]
Percentage of reserves produced from wells in certain formations	77.00%
Delaware Basin
Reserve Quantities [Line Items]
Percentage of reserves produced from wells in certain formations	23.00%

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Discount rate of future cash flows

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Estimated extensions and discoveries of reserves associated with new wells

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Percentage of proved undeveloped reserves.

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Percentage of reserves produced from wells in certain formations.

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Proved Developed Reserve, Revision of Previous Estimate

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Revisions as a percentage of beginning of the years reserves balance.

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Unweighted arithmetic average first-day-of-the-month prices

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Energy measure of increase in quantity of proved reserve of oil and gas resulting from the extension of the proved acreage of previously discovered reservoir or discovery of new field with proved reserve or of new reservoir of proved reserve in old field, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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Energy measure of increase in quantity of proved reserve of oil and gas resulting from purchase of mineral in place, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-Name Form 20-F
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Energy measure of increase (decrease) in quantity of proved reserve of oil and gas related to revision of a previous estimate resulting from new information, except for an increase in proved acreage, or change in economic factors, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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Energy measure of decrease in quantity of proved reserve of oil and gas resulting from sale of mineral in place, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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