Assets and Liabilities Measured at Fair Value (Tables)

12 Months Ended

Dec. 31, 2014

Assets and Liabilities Measured at Fair Value [Abstract]

Carrying Value of Assets and Liabilities Recorded at Fair Value on Recurring Basis

			Fair Value Measurements at Reporting Date Using
(Thousands of dollars)	Fair Value at December 31, 2014		Quoted Prices in Active Markets for Identical Assets (Liabilities) (Level 1)	Significant Other Observable Inputs (Level 2)	Significant Unobservable Inputs (Level 3)
Assets
Commodity derivative contracts	$	23,168	–	23,168	–
Liabilities
Nonqualified employee savings plan	$	(14,408)	(14,408)	–	–
Foreign currency exchange              derivative contracts		(25)	–	(25)	–
Total	$	(14,433)	(14,408)	(25)	–
			Fair Value Measurements at Reporting Date Using
(Thousands of dollars)	Fair Value at December 31, 2013		Quoted Prices in Active Markets for Identical Assets (Liabilities) (Level 1)	Significant Other Observable Inputs (Level 2)	Significant Unobservable Inputs (Level 3)
Assets
Commodity derivative contracts	$	1,970	–	1,970	–
Liabilities
Nonqualified employee savings plan	$	(13,267)	(13,267)	–	–
Foreign currency exchange              derivative contracts		(1,038)	–	(1,038)	–
Total	$	(14,305)	(13,267)	(1,038)	–

Carrying Amounts and Estimated Fair Values of Financial Instruments

	At December 31,
	2014			2013
(Thousands of dollars)	Carrying Amount		Fair Value	Carrying Amount	Fair Value
Financial assets (liabilities):
Canadian government securities with maturities             greater than 90 days at the date of acquisition	$	461,313	462,056	374,842	375,623
Current and long-term debt		(3,001,626)	(2,774,065)	(2,962,812)	(2,822,827)