Other Financial Information (Noncash Opearting Working Capital (Increase) Decrease) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Other Financial Information [Abstract]
(Increase) decrease in accounts receivable	$ (15,528)	$ 125,283
Decrease in inventories	16,929	5,918
(Increase) decrease in prepaid expenses	(7,890)	9,206
Increase (decrease) in accounts payable and accrued liabilities	49,311	(136,500)
Increase in income taxes payable	42,618	38,674
Net decrease in noncash operating working capital	85,440	42,581
Cash income taxes paid, net of refunds	36,618	9,448
Interest paid, net of amounts capitalized of $2,377 in 2018 and $2,449 in 2017	79,279	72,136
Asset retirement costs capitalized	1,608	797
Decrease in capital expenditure accrual	39,322	43,370
Interest paid, amounts capitalized	$ 2,377	$ 2,449