Long Term Debt (Tables)

9 Months Ended

Sep. 30, 2017

Debt Disclosure [Abstract]

Components of Long-term Debt

The components of long-term debt as of the dates indicated below were as follows:

	September 30, 2017				December 31, 2016
	Principal		Unamortized Debt Issuance Debt Cost		Principal		Unamortized Debt Issuance Debt Cost
	(Thousands of dollars)
Senior Notes issued March 17, 2014, interest only payable semi-annually at 5.25%, maturing March 15, 2019	$	500,000	$	1,818	$	500,000	$	2,753
Revolving Credit Facility due October 1, 2018 with a group of commercial banks, interest payable at variable rates	100,000		—		134,000		—
Total long-term debt	$	600,000	$	1,818	$	634,000	$	2,753