Long Term Debt (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Components of Long-term Debt

The components of long-term debt as of December 31 were as follows:

	December 31, 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	$	1,506	$	500,000	$	2,753
Revolving Credit Facility due March 7, 2019 with a group of commercial banks, interest payable at variable rates	117,500		—		134,000		—
Total long-term debt	$	617,500	$	1,506	$	634,000	$	2,753

Summary of Annual Maturities of Long-term Debt

Listed below is information on our future annual maturities of long-term debt (in thousands):

2018	$	—
2019	617,500
2020	—
2021	—
2022	—
Thereafter	—
Total	$	617,500