Long-term Debt (Tables)

12 Months Ended

Dec. 31, 2016

Financing Arrangements [Abstract]

Schedule of Long-term Debt

	December 31,
(Thousands of dollars)	2016		2015
Notes payable
2.50% notes, due December 2017*	$	550,000	550,000
4.00% notes, due June 2022		500,000	500,000
3.70% notes, due December 2022*		600,000	600,000
6.875% notes, due August 2024		550,000	-
7.05% notes, due May 2029		250,000	250,000
5.125% notes, due December 2042*		350,000	350,000
Notes payable to banks, 1.4375% at December 31		-	600,000
Total notes payable		2,800,000	2,850,000
Unamortized discount on notes payable		(23,835)	(19,223)
Total notes payable, net of unamortized discount		2,776,165	2,830,777
Capitalized lease obligation, due through March 2029		216,402	228,698
Total debt including current maturities		2,992,567	3,059,475
Current maturities		(569,817)	(18,881)
Total long-term debt	$	2,422,750	3,040,594

*The interest rate paid is 1.0%aboverate shown due to a downgrade of the credit rating for the Company’s notes in February 2016.