Financial Instruments and Risk Management (Tables)

12 Months Ended

Dec. 31, 2017

Financial Instruments and Risk Management [Abstract]

Fair Value of Derivative Instruments Not Designated as Hedging Instruments

	December 31, 2017			December 31, 2016
(Thousands of dollars)	Asset (Liability) Derivatives			Asset (Liability) Derivatives
Type of Derivative Contract	Balance Sheet Location		Fair Value	Balance Sheet Location		Fair Value
Commodity	Accounts payable	$	(39,093)	Accounts payable	$	(48,864)
Foreign exchange	–		–	Accounts payable	$	(73)

Recognized Gains and Losses for Derivative Instruments Not Designated as Hedging Instruments

		Gain (Loss)
(Thousands of dollars)			Year Ended December 31,
Type of Derivative Contract	Statement of Operations Locations	2017		2016
Commodity	Sales and other operating revenues	$	9,567	$	(63,412)
Foreign exchange	Interest and other income (loss)		–		26,714
		$	9,567	$	(36,698)