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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$ (2,223)	$ (13,573)	$ (69,349)	$ 50,438
Commodity Derivative Contracts [Member] | Gain (Loss) on Crude Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$ (2,223)	$ (13,573)	$ (69,349)	50,365
Foreign Exchange Derivative Contracts [Member] | Interest And Other Income (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)				$ 73