Other Financial Information (Noncash Operating Working Capital (Increase) Decrease) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net (increase) decrease in operating working capital, excluding cash and cash equivalents:
(Increase) decrease in accounts receivable	$ (16,954)	$ 186,436
Decrease in inventories	392	7,553
(Increase) in prepaid expenses	(3,652)	(10,179)
Increase (decrease) in accounts payable and accrued liabilities	11,810	(76,287)
Increase (decrease) in income taxes payable	(648)	304
Net (increase) decrease in noncash operating working capital	(9,052)	107,827
Supplementary disclosures:
Cash income taxes paid, net of refunds	720	72
Interest paid, net of amounts capitalized of $3.3 million in 2021 and $2.4 million in 2020	44,577	42,344
Capitalized interest paid	3,300	2,400
Non-cash investing activities:
Asset retirement costs capitalized	6,390	280
Decrease in capital expenditure accrual	13,617	$ 10,633
Impairment of asset retirement obligation	$ 74,400