Incentive Plans (Tables)

9 Months Ended

Sep. 30, 2017

Incentive Plans [Abstract]

Share-Based Plans, Amounts Recognized

	Nine Months Ended
	September 30,
(Thousands of dollars)		2017	2016
Compensation charged against income (loss) before tax benefit	$	28,264	35,948
Related income tax benefit recognized in income		8,695	11,796