Derivative Instruments and Fair Value Measurements - Fair Value Measurements (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives:
Current assets	$ 263	$ 166
Current assets, counterparty offsets	0	0
Current liabilities	(247)	(145)
Current liabilities, counterparty offsets	0	0
Net value	16	21
Net value, counterparty offsets	0	0
Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1)
Derivatives:
Current assets	0	0
Current liabilities	0	0
Net value	0	0
Significant Other Observable Inputs (Level 2)
Derivatives:
Current assets	263	166
Current liabilities	(247)	(145)
Net value	16	21
Significant Unobservable Inputs (Level 3)
Derivatives:
Current assets	0	0
Current liabilities	0	0
Net value	$ 0	$ 0

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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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were offset against collateral under a master netting arrangement.

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Fair value, after the effects of master netting arrangements, of a financial liability or 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 liabilities not subject to a master netting arrangement and not elected to be offset.

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