Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2017

Incentive Plans [Abstract]

Share-Based Plans, Amounts Recognized

	Three Months Ended
	March 31,
(Thousands of dollars)		2017	2016
Compensation charged against income before tax benefit	$	8,148	9,988
Related income tax benefit recognized in income		2,529	3,251