Asset Retirement Obligations (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014
Asset Retirement Obligation [Abstract]
Carrying Amount at Beginning of Period		$ 752,718	$ 761,898
Liabilities Incurred		19,990	54,819
Liabilities Settled (1)	[1]	(9,891)	(25,478)
Accretion		15,815	23,346
Revisions		18,156	13,859
Foreign Currency Translations		(1,009)	2,506
Carrying Amount at End of Period		795,779	830,950
Current Portion		10,993	28,498
Noncurrent Portion		$ 784,786	$ 802,452

[1] Includes settlements related to asset sales.