Long-term Debt (Tables)

12 Months Ended

Dec. 31, 2015

Financing Arrangements And Long-Term Debt [Abstract]

Schedule of Long-term Debt

	December 31,
(Thousands of dollars)	2015		2014*
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
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, 2015		600,000	450,000
Total notes payable		2,850,000	2,700,000
Unamortized discount on notes payable		(19,223)	(23,522)
Total notes payable, net of unamortized discount		2,830,777	2,676,478
Capitalized lease obligation, due through June 2029		228,698	306,579
Total debt including current maturities		3,059,475	2,983,057
Current maturities		(18,881)	(465,388)
Total long-term debt	$	3,040,594	2,517,669