Asset Retirement Obligations (Schedule of Reconciliation of Beginning and Ending Aggregate Carrying Amount of Asset Retirement Obligations) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Asset Retirement Obligations [Abstract]
Balance at beginning of year		$ 825,312	$ 875,728
Accretion expense		46,742	48,665	$ 50,778
Liabilities incurred		13,690	76,775
Revision of previous estimates		(4,511)	(85,504)
Liabilities settled		(20,589)	(13,359)
Liabilities assumed by purchaser of oil and gas assets		(91,883)	(33,448)
Changes due to translation of foreign currencies		12,296	(43,545)
Balance at end of year		$ 825,312	$ 875,728	$ 875,728	$ 781,057	$ 825,312
Liabilities reported as held for sale at end of year	[1]				(85,900)
Current portion of liability at end of year	[2]				(13,629)	(31,838)
Noncurrent portion of liability at end of year					$ 681,528	$ 793,474	[3]

[1] Liabilities held for sale related to Seal properties in Canada which were sold in January 2017.

[2] Included in Other Accrued Liabilities on the Consolidated Balance Sheet.

[3] Reclassified to conform to current presentation. See Note B for additional information.