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	Sep. 30, 2020	Dec. 31, 2019
Accounts receivable
Derivatives, Fair Value [Line Items]
Asset (Liability) Derivatives	$ 93,774
Accounts payable
Derivatives, Fair Value [Line Items]
Asset (Liability) Derivatives		$ (33,364)