Financial Instruments and Risk Management (Recognized Gains and Losses for Derivative Instruments Not Designated as Hedging Instruments) (Details) - Nondesignated [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$ (29,502)	$ 37,302
Commodity Derivative Contracts [Member] | Gain (Loss) on Crude Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$ (29,502)	37,077
Foreign Exchange Derivative Contracts [Member] | Interest And Other Income (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)		$ 225