Other Financial Information (Noncash Operating Working Capital (Increase) Decrease) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Net (increase) decrease in operating working capital, excluding cash and cash equivalents:
(Increase) decrease in accounts receivable	$ 251,706	$ (128,698)
Decrease in inventories	4,747	4,398
(Increase) in prepaid expenses	(17,400)	(3,745)
Increase (decrease) in accounts payable and accrued liabilities	(264,078)	165,224
Increase (decrease) in income taxes payable	(1,236)	3,078
Net (increase) decrease in noncash operating working capital	(26,261)	40,257
Supplementary disclosures:
Cash income taxes paid, net of refunds	(12,559)	(4,563)
Interest paid, net of amounts capitalized of $5.9 million in 2020 and $0.2 million in 2019	139,651	137,116
Capitalized interest paid	5,900	200
Non-cash investing activities:
Asset retirement costs capitalized	6,342	48,203
(Increase) decrease in capital expenditure accrual	$ 74,742	(52,659)
Asset retirement obligations assumed		$ (37,300)