Acquisition - Additional Information (Detail) shares in Millions, $ in Millions		6 Months Ended
Jan. 18, 2018 USD ($) a Well shares	Jun. 30, 2018
Flat Castle Acquisition [Member]
Business Acquisition [Line Items]
Area of land purchased \| a	44,500
Purchase price	$ 90
Purchase price paid through shares of common stock \| shares	37.8
Transaction costs capitalized related to acquisition	$ 1
Flat Castle Acquisition [Member] \| Proved Oil And Gas Properties [Member]
Business Acquisition [Line Items]
Number of producing wells acquired \| Well	1
Purchase price	$ 4
Flat Castle Acquisition [Member] \| Unproved Oil and Natural Gas Properties [Member]
Business Acquisition [Line Items]
Purchase price	$ 86
Cardinal Midstream II, LLC [Member]
Business Acquisition [Line Items]
Acquisition completed month and year		2018-07

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
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-URI http://asc.fasb.org/extlink&oid=109124213&loc=d3e6613-128477

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=109124213&loc=d3e6578-128477

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