Incentive Plans (Tables)

6 Months Ended

Jun. 30, 2017

Incentive Plans [Abstract]

Share-Based Plans, Amounts Recognized

	Six Months Ended
	June 30,
(Thousands of dollars)		2017	2016
Compensation charged against income (loss) before tax benefit	$	16,722	24,288
Related income tax benefit recognized in income		5,425	8,210