Financial Instruments and Risk Management (Tables)

12 Months Ended

Dec. 31, 2018

Financial Instruments and Risk Management [Abstract]

Fair Value of Derivative Instruments Not Designated as Hedging Instruments

	December 31, 2018			December 31, 2017
(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 receivable	$	3,837	Accounts payable	$	(39,093)

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	2018		2017	2016
Commodity	(Loss) gain on crude contracts	$	(41,975)	9,566	(63,412)
Foreign exchange	Interest and other income (loss)		–	–	26,714
		$	(41,975)	9,566	(36,698)