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, 2018	Dec. 31, 2017		Dec. 31, 2016
Asset Retirement Obligations [Abstract]
Balance at beginning of year	$ 722,139	$ 781,057
Accretion expense	44,559	42,590	[1]	$ 46,742	[1]
Liabilities incurred	13,886	52,331
Liabilities assumed from PAI	359,643
Revisions of previous estimates	(24,959)	(47,612)
Liabilities settled	(23,398)	(29,111)
Liabilities assumed by purchaser of oil and gas assets		(87,456)
Changes due to translation of foreign currencies	(8,966)	10,340
Balance at end of year	$ 1,082,904	$ 722,139		$ 781,057

[1] Reclassified to conform to current presentation (see Note B).