Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2019

Incentive Plans [Abstract]

Share-Based Plans, Amounts Recognized

	Three Months Ended
	March 31,
(Thousands of dollars)		2019	2018
Compensation charged against income before tax benefit	$	15,514	7,549
Related income tax benefit recognized in income		2,342	894