Other Financial Information (Noncash Opearting Working Capital (Increase) Decrease) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Other Financial Information [Abstract]
(Increase) decrease in accounts receivable	$ (31,178)	$ 90,614
Decrease in inventories	16,732	5,869
(Increase) decrease in prepaid expenses	(8,695)	25,285
Increase (decrease) in accounts payable and accrued liabilities	17,946	(115,977)
Increase (decrease) in income taxes payable	2,645	(4,721)
Net (increase) decrease in noncash operating working capital	(2,550)	1,070
Cash income taxes paid, net of refunds	77,508	25,118
Interest paid, net of amounts capitalized of $3,719 in 2018 and $3,338 in 2017	115,009	95,899
Asset retirement costs capitalized	2,907	38,992
(Increase) decrease in capital expenditure accrual	(751)	42,403
Interest paid, amounts capitalized	$ 3,719	$ 3,338