Financial Instruments and Risk Management (Tables)

9 Months Ended

Sep. 30, 2018

Financial Instruments and Risk Management [Abstract]

Fair Value of Derivative Instruments Not Designated as Hedging Instruments

	September 30, 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 payable	$	(44,601)	Accounts payable	$	(39,093)

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

			Gain (Loss)
		Three Months Ended			Nine Months Ended
(Thousands of dollars)		September 30,			September 30,
Type of Derivative Contract	Statement of Operations Location		2018	2017	2018	2017
Commodity	Gain (loss) on crude contracts	$	(2,223)	(13,573)	(69,349)	50,365
Foreign exchange	Interest and other income (loss)		–	–	–	73
		$	(2,223)	(13,573)	(69,349)	50,438

Carrying Value of Assets and Liabilities Recorded at Fair Value on Recurring Basis

	September 30, 2018					December 31, 2017
(Thousands of dollars)	Level 1		Level 2	Level 3	Total	Level 1	Level 2	Level 3	Total
Liabilities:
Nonqualified employee         savings plans	$	15,957	–	–	15,957	16,158	–	–	16,158
Commodity derivative contracts		–	44,601	–	44,601	–	39,093	–	39,093
	$	15,957	44,601	–	60,558	16,158	39,093	–	55,251