Other Financial Information (Noncash Operating Working Capital (Increase) Decrease) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other Financial Information [Abstract]
(Increase) decrease in accounts receivable	$ (112,673)	$ 4,227
Decrease in inventories	3,930	15,637
(Increase) decrease in prepaid expenses	(10,763)	3,446
Increase (decrease) in accounts payable and accrued liabilities	21,131	(26,908)
Increase (decrease) in income taxes payable	(130)	45
Net (increase) decrease in noncash operating working capital	(98,505)	(3,553)	[1]
Cash income taxes paid, net of refunds		(1,104)
Interest paid, net of amounts capitalized of $0 in 2019 and 2018	39,024	35,158
Asset retirement costs capitalized	486	727
(Increase) decrease in capital expenditure accrual	(63,328)	(17,592)
Interest paid, amounts capitalized	$ 0	$ 0

[1] Reclassified to conform to current presentation (see Note A).