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, 2019	Dec. 31, 2018
Accounts payable
Derivatives, Fair Value [Line Items]
Liabilities	$ (33,364)
Accounts receivable
Derivatives, Fair Value [Line Items]
Asset		$ 3,837