Financial Instruments and Risk Management (Tables)

3 Months Ended

Mar. 31, 2018

Financial Instruments and Risk Management [Abstract]

Fair Value of Derivative Instruments Not Designated as Hedging Instruments

	March 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 payable	$	(53,444)	Accounts payable	$	(39,093)

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

			Gain (Loss)
		Three Months Ended
(Thousands of dollars)		March 31,
Type of Derivative Contract	Statement of Operations Location		2018	2017
Commodity	Gain (loss) on crude contracts	$	(29,502)	37,077
Foreign exchange	Interest and other income (loss)		–	225
		$	(29,502)	37,302

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

	March 31, 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	$	15,756	–	–	15,756	16,158	–	–	16,158
Commodity derivative contracts		–	53,444	–	53,444	–	39,093	–	39,093
	$	15,756	53,444	–	69,200	16,158	39,093	–	55,251