Assets and Liabilities Measured at Fair Value (Tables)

12 Months Ended

Dec. 31, 2016

Assets and Liabilities Measured at Fair Value [Abstract]

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

	December 31, 2016					December 31, 2015
(Thousands of dollars)	Level 1		Level 2	Level 3	Total	Level 1	Level 2	Level 3	Total
Assets:
Commodity derivative         contracts		–	–	–	–	–	89,358	–	89,358
	$	–	–	–	–	–	89,358	–	89,358
Liabilities:
Nonqualified employee         savings plans	$	13,904	–	–	13,904	12,971	–	–	12,971
Commodity derivative contracts		–	48,864	–	48,864	–	–	–	–
Foreign currency exchange         derivative contracts		–	73	–	73	–	29	–	29
	$	13,904	48,937	–	62,841	12,971	29	–	13,000

Carrying Amounts and Estimated Fair Values of Financial Instruments

	At December 31,
	2016			2015
(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	$	111,542	111,331	173,288	173,234
Current and long-term debt		(2,992,567)	(2,951,992)	(3,059,475)	(2,189,858)

Nonrecurring Fair Value Measurements

	Year Ended December 31, 2016
						Total
					Net Book	Pretax
					Value	(Noncash)
	Fair Value				Prior to	Impairment
(Thousands of dollars)		Level 1	Level 2	Level 3	Impairment	Expense
Assets:
Impaired proved properties
Canada		–	–	71,967	167,055	95,088
	$	–	–	71,967	167,055	95,088

	Year Ended December 31, 2015
						Total
					Net Book	Pretax
					Value	(Noncash)
	Fair Value				Prior to	Impairment
(Thousands of dollars)		Level 1	Level 2	Level 3	Impairment	Expense
Assets:
Impaired proved properties
Gulf of Mexico	$	–	–	316,106	645,088	328,982
Western Canada		–	–	23,526	707,100	683,574
Malaysia		–	–	1,200,900	2,681,500	1,480,600
	$	–	–	1,540,532	4,033,688	2,493,156