Supplemental Oil and Gas Reserve Information - Unaudited - Additional Information (Detail)	12 Months Ended
Dec. 31, 2017 MBoe $ / bbl $ / MMBTU	Dec. 31, 2016 location MBoe $ / bbl $ / MMBTU	Dec. 31, 2015 MBoe $ / bbl $ / MMBTU
Reserve Quantities [Line Items]
Net positive (negative) revisions of previous estimates (MMBoe)	(19,200)	31,136	(84,635)
Positive (negative) revisions of previous estimates - proved developed reserves (MMBoe)	(14,200)
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe)	(5,000)
Proved undeveloped locations \| location		259
Proved undeveloped locations, net \| location		190.8
Additions due to extensions and discoveries (Energy)	51,153	14,876	46,640
Estimated extensions and discoveries of reserves associated with new wells (Energy)	17,900	6,200	20,400
Additional proved undeveloped reserves (Energy)	33,300	6,500	26,300
Percentage of reserves produced from wells in certain formations	100.00%	100.00%	100.00%
Percentage of proved undeveloped reserves		100.00%	100.00%
Divested reserves associated with non-operated properties (Energy)	1,387	7,635	0
Purchases of reserves in place (Energy)	671	66,936	2,565
Percentage of net positive (negative) revisions	(6.00%)	14.00%	(31.00%)
Proved undeveloped reserves, decrease (Energy)		71,500
Discount rate of future cash flows	10.00%
Unweighted arithmetic average first-day-of-the-month prices for oil, price per Bbl \| $ / bbl	51.34	42.60	50.16
Unweighted arithmetic average first-day-of-the-month prices for natural gas, price per MMBtu \| $ / MMBTU	2.99	2.47	2.63
Revision Due to Performance
Reserve Quantities [Line Items]
Net positive (negative) revisions of previous estimates (MMBoe)	(39,100)	30,400	1,900
Positive (negative) revisions of previous estimates - proved developed reserves (MMBoe)	(29,700)
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe)	(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)	(2,100)	(9,500)
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe)	(1,800)
Revision of Previous Estimate Due to Realized Prices
Reserve Quantities [Line Items]
Net positive (negative) revisions of previous estimates (MMBoe)	16,100	(8,200)	(17,200)
Positive (negative) revisions of previous estimates - proved developed reserves (MMBoe)	14,100
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe)	2,000
Revision of Previous Estimate Due to Ownership Adjustments
Reserve Quantities [Line Items]
Net positive (negative) revisions of previous estimates (MMBoe)	2,500	8,200	3,000
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe)	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

Additional proved undeveloped reserves

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

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Proved Undeveloped Reserve, Revision of Previous Estimate

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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).

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

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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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