Derivative Instruments - Summary of Location and Fair Value of Derivative Instruments (Details) - Commodity swaps - Current derivative assets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Gross Amount Recognized	$ 162	$ 1,057
Less Group Amount of Offset	0	0
Net Amount Recognized	$ 162	$ 1,057

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

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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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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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