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, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014
Asset Retirement Obligations [Abstract]
Balance at beginning of year		$ 875,728	$ 880,003
Accretion expense		48,665	50,778	$ 48,996
Liabilities incurred		76,775	70,568
Revision of previous estimates		(85,504)	8,278
Liabilities settled		(13,359)	(36,818)
Liabilities assumed by purchases of oil and gas assets		(33,448)	(69,416)
Changes due to translation of foreign currencies		(43,545)	(27,665)
Balance at end of year		$ 875,728	$ 880,003	$ 880,003	$ 825,312	$ 875,728
Current portion of liability at end of year	[1]				(31,838)	(34,202)
Noncurrent portion of liability at end of year					$ 793,474	$ 841,526	[2]

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

[2] Reclassified to conform to current presentation.