Asset Retirement Obligations (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Asset Retirement Obligations, Noncurrent [Abstract]
Carrying Amount at Beginning of Period		$ 811,554	$ 752,718
Liabilities Incurred	[1]	212,739	63,844
Liabilities Settled	[2]	(94,800)	(17,415)
Accretion		32,306	31,956
Revisions		(38,286)	(13,356)
Foreign Currency Translations		(10,587)	(6,193)
Carrying Amount at End of Period		912,926	811,554
Current Portion		18,516	7,651
Noncurrent Portion		$ 894,410	$ 803,903

[1] Includes $164 million related to Yates transaction (see Note 17).

[2] Includes settlements related to asset sales.