Cash Flow Disclosures (Tables)

3 Months Ended

Mar. 31, 2016

Cash Flow Disclosures [Abstract]

Cash Flow Activities

	Three Months Ended March 31
(Thousands of dollars)	2016		2015
Net (increase) decrease in operating working capital other than    cash and cash equivalents:
Decrease in accounts receivable	$	2,354	302,602
Decrease (increase) in inventories		1,667	(60,562)
Decrease (increase) in prepaid expenses		98,888	(6,825)
Decrease in deferred income tax assets		6,134	5,040
Decrease in accounts payable and accrued liabilities		(225,309)	(17,281)
Increase in current income tax liabilities		11,919	35,833
Net (increase) decrease in noncash operating working capital	$	(104,347)	258,807
Supplementary disclosures:
Cash income taxes paid, net of refunds	$	(7,865)	28,280
Interest paid, net of amounts capitalized		1,849	(64)
Non-cash investing activities:
Asset retirement costs capitalized	$	3,723	6,380
Decrease in capital expenditure accrual		81,858	239,572