Incentive Plans (Tables)

9 Months Ended

Sep. 30, 2016

Incentive Plans [Abstract]

Share-Based Plans, Amounts Recognized

	Nine Months Ended
	September 30,
(Thousands of dollars)		2016	2015
Compensation charged against income before tax benefit	$	35,948	30,722
Related income tax benefit recognized		11,796	9,046