Other Financial Information (Noncash Operating Working Capital (Increase) Decrease) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Net (increase) decrease in operating working capital, excluding cash and cash equivalents:
(Increase) decrease in accounts receivable	$ (104,775)	$ 227,710
Decrease in inventories	8,938	13,968
(Increase) in prepaid expenses	(1,945)	(20,712)
Increase (decrease) in accounts payable and accrued liabilities	124,699	(219,228)
(Decrease) in income taxes payable	(352)	(403)
Net decrease in noncash operating working capital	26,565	1,335
Supplementary disclosures:
Cash income taxes paid, net of refunds	1,474	(7)
Interest paid, net of amounts capitalized of $7.4 million in 2021 and $4.9 million in 2020	80,546	100,745
Capitalized interest paid	7,400	4,900
Non-cash investing activities:
Asset retirement costs capitalized	6,669	6,342
Decrease in capital expenditure accrual	20,614	$ 58,602
Impairment of asset retirement obligation	$ 74,400