Other Financial Information (Noncash Operating Working Capital (Increase) Decrease) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Financial Information [Abstract]
Accounts receivable	$ 297,625	$ 175,820	$ 224,281
Inventories	(15,340)	25,697	14,166
Prepaid expenses	(144,845)	6,575	195,013
Deferred income tax assets	3,924	6,884	15,510
Accounts payable and accrued liabilities	(36,887)	(54,785)	(176,543)
Current income tax liabilities	(69,413)	(163,920)	(6,098)
Net (increase) decrease in noncash operating working capital	35,064	(3,729)	266,329
Cash income taxes paid, net of refunds	118,667	573,799	457,006
Interest paid, net of amounts capitalized	110,386	114,232	60,501
Asset retirement costs capitalized	76,775	70,568	172,488
Decrease (increase) in capital expenditure accrual	$ 462,474	$ 93,080	$ (197,054)