Stock-Based Compensation (Tables)

9 Months Ended

Sep. 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 nine months and quarters ended September 30, 2016 and 2015.

	Quarter Ended September 30,				Nine Months Ended September 30,
	2016		2015		2016		2015
	(Thousands of dollars)
Stock-based compensation expense:
Time-based restricted stock units	$	631	$	619	$	1,847	$	1,827
Performance-based restricted stock units		823		1,081		2,502		3,232
Total stock-based compensation expense	$	1,454	$	1,700	$	4,349	$	5,059