Assets and Liabilities Measured at Fair Value (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

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

The fair value measurements for these assets and liabilities at December 31, 2020 and 2019 are presented in the following table

	December 31, 2020					December 31, 2019
(Thousands of dollars)	Level 1		Level 2	Level 3	Total	Level 1	Level 2	Level 3	Total
Assets:
Commodity derivative contracts	$	—	13,050	—	13,050	—	—	—	—
	$	—	13,050	—	13,050	—	—	—	—
Liabilities:
Nonqualified employee savings plans	$	14,988	—	—	14,988	17,035	—	—	17,035
Commodity derivative contracts	—		102,675	—	102,675	—	33,364	—	33,364
Contingent consideration	—		—	133,004	133,004	—	—	146,787	146,787
	$	14,988	102,675	133,004	250,667	17,035	33,364	146,787	197,186

Carrying Amounts and Estimated Fair Values of Financial Instruments

The following table presents the carrying amounts and estimated fair values of financial instruments held by the Company at December 31, 2020 and 2019.  The fair value of a financial instrument is the amount at which the instrument could be exchanged in a current transaction between willing parties.  The table excludes cash and cash equivalents, trade accounts receivable, trade accounts payable and accrued expenses, all of which had fair values approximating carrying amounts.  The fair value of current and long-term debt was estimated based on rates offered to the Company at that time for debt of the same maturities.  The Company has off-balance sheet exposures relating to certain letters of credit.  The fair value of these, which represents fees associated with obtaining the instruments, was nominal.

	December 31,
	2020			2019
(Thousands of dollars)	Carrying Amount		Fair Value	Carrying Amount	Fair Value
Financial assets (liabilities):
Current and long-term debt	$	(2,988,067)	(2,948,171)	(2,803,381)	(3,074,929)

Nonrecurring Fair Value Measurements

The fair value information associated with these impaired properties is presented in the following table

	Years Ended December 31, 2020
					Net Book Value Prior to Impairment	Total Pretax Impairment
	Fair Value
(Thousands of dollars)	Level 1		Level 2	Level 3
Assets:
Impaired proved properties
U.S. Offshore	$	—	—	2,618,001	3,770,516	1,152,515
Other Foreign	—		—	42,980	82,689	39,709
Corporate	—		—	58,199	72,259	14,060