Financing Arrangements and Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2018

Financing Arrangements and Long-Term Debt [Abstract]

Schedule of Long-term Debt

	December 31,
(Thousands of dollars)	2018		2017
Notes payable
4.00% notes, due June 2022	$	500,000	500,000
4.45% notes, due December 20221		600,000	600,000
6.875% notes, due August 2024		550,000	550,000
5.75% notes, due August 2025		550,000	550,000
7.05% notes, due May 2029		250,000	250,000
5.875% notes, due December 20421		350,000	350,000
Total notes payable		2,800,000	2,800,000
Unamortized debt issuance cost and discount on notes payable		(23,627)	(27,433)
Total notes payable, net of unamortized discount		2,776,373	2,772,567
Capitalized lease obligation, due through March 2029		136,344	143,855
Total debt including current maturities		2,912,717	2,916,422
Senior Unsecured Revolving Credit Facility		325,000	-
Current maturities		(10,583)	(9,902)
Total long-term debt	$	3,227,134	2,906,520

1Due to a series of ratings changes by credit agencies, the paying interest rates on the notes due December 2022 and December 2042 decreased from 4.7% to 4.45% and 6.125% to 5.875%, respectively, in 2017 and remained through 2018.