Fair Value of Derivative Instruments on Condensed Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative Asset, Current	$ 33	$ 0
Derivative liabilities	63,257	27,777
Derivative Asset, Noncurrent	54	0
Derivative assets	87	0
Derivative Liability, Noncurrent	29,566	13,900
Derivative Liability	92,823	41,677
Commodity contracts
Derivatives, Fair Value [Line Items]
Derivative Liability	92,700
Commodity contracts \| Current Derivative Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Current	33	0
Derivative liabilities	63,257	27,777
Commodity contracts \| Noncurrent Derivative Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Noncurrent	54	0
Derivative Liability, Noncurrent	$ 29,566	$ 13,900

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. Includes assets not subject to a master netting arrangement and not elected to be offset.

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