Commodity Derivative Financial Instruments - Summary of Fair Value and Classification of Derivative Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Derivatives Fair Value [Line Items]
Gross fair value, assets	$ 19,741	$ 50,264
Effect of counterparty netting, assets	(4,343)	(2,226)
Net carrying value on balance sheet, assets	15,398	48,038
Gross fair value, liabilities	4,520	2,226
Effect of counterparty netting, liabilities	(4,343)	(2,226)
Net carrying value on balance sheet, liabilities	177	0
Commodity Derivative Assets, Current
Derivatives Fair Value [Line Items]
Gross fair value, assets	19,028	38,746
Effect of counterparty netting, assets	(4,238)	(776)
Net carrying value on balance sheet, assets	14,790	37,970
Deferred Charges and Other Long-term Assets
Derivatives Fair Value [Line Items]
Gross fair value, assets	713	11,518
Effect of counterparty netting, assets	(105)	(1,450)
Net carrying value on balance sheet, assets	608	10,068
Commodity Derivative Liabilities, Current
Derivatives Fair Value [Line Items]
Gross fair value, liabilities	4,397	776
Effect of counterparty netting, liabilities	(4,238)	(776)
Net carrying value on balance sheet, liabilities	159	0
Commodity Derivative Liabilities, Long-term
Derivatives Fair Value [Line Items]
Gross fair value, liabilities	123	1,450
Effect of counterparty netting, liabilities	(105)	(1,450)
Net carrying value on balance sheet, liabilities	$ 18	$ 0

Fair value of liability associated with 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.

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