Financial Instruments and Risk Management - Fair Value of Derivative Instruments Not Designated as Hedging Instruments (Details) - Not Designated as Hedging Instrument - Commodity derivative contracts - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts payable
Derivatives, Fair Value [Line Items]
Liability	$ (89,842)	$ (33,364)
Deferred credits and other liabilities
Derivatives, Fair Value [Line Items]
Liability	(12,833)
Accounts receivable
Derivatives, Fair Value [Line Items]
Asset	$ 13,050