Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2016

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Share Based Compensation Expense

The table below sets forth the total amount of stock-based compensation expense for the six months and quarters ended June 30, 2016 and 2015.

	Quarter Ended				Six Months Ended
	June 30,				June 30,
	2016		2015		2016		2015
	(Thousands of dollars)
Stock-based compensation expense:
Time-based restricted units	$	597	$	571	$	1,216	$	1,208
Performance-based restricted units		809		1,069		1,680		2,151
Total stock-based compensation expense	$	1,406	$	1,640	$	2,896	$	3,359