Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2014

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 quarters and nine months ended September 30, 2014 and 2013.

	Quarter Ended September 30,				Nine Months Ended September 30,
	2014		2013		2014		2013
			(Thousands of dollars)
Stock-based compensation expense:
Time-based restricted units	$	584	$	120	$	1,033	$	342
Performance-based restricted units		975		558		2,256		1,335
Total stock-based compensation expense	$	1,559	$	678	$	3,289	$	1,677