Commodity Derivative Financial Instruments - Summary of Change in Fair Values of Derivative (Details) - Derivatives Not Designated as Hedging Instruments [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2018
Derivative [Line Items]
Unrealized gain (loss) of open non-hedge derivative instruments	$ (944)	$ (1,151)
Realized gain (loss) on settlement of non-hedge derivative instruments	(256)	(305)
Gain (loss) on commodity derivative instruments	$ (1,200)	$ (1,456)