Debt (Tables)

6 Months Ended

Jun. 30, 2018

Debt Disclosure [Abstract]

Components of Debt

Listed below is information regarding our indebtedness, all of which was classified as short-term debt on our balance sheet as of June 30, 2018 and as long-term debt on our balance sheet as of December 31, 2017:

	June 30, 2018				December 31, 2017
	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	$	1,229	$	500,000	$	1,506
Revolving Credit Facility due March 7, 2019 with a group of commercial banks, interest payable at variable rates	122,220		—		117,500		—
Total indebtedness	$	622,220	$	1,229	$	617,500	$	1,506