Summary of Significant Accounting Policies - Schedule of Derivative Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Assets, Fair Value	$ 62,277	$ 15,401
Assets, Fair Value	21,983
Derivative Financial Instruments – current
Derivative [Line Items]
Assets, Fair Value	62,277	15,401
Derivative Financial Instruments – current \| Natural Gas Price Derivatives
Derivative [Line Items]
Assets, Fair Value	60,002	6,096
Derivative Financial Instruments – current \| Oil Price Derivatives
Derivative [Line Items]
Assets, Fair Value	2,275	$ 9,305
Derivative Financial Instruments – long-term
Derivative [Line Items]
Assets, Fair Value	21,983
Derivative Financial Instruments – long-term \| Natural Gas Price Derivatives
Derivative [Line Items]
Assets, Fair Value	21,118
Derivative Financial Instruments – long-term \| Oil Price Derivatives
Derivative [Line Items]
Assets, Fair Value	$ 865

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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