Asset Retirement Obligations (Schedule of Reconciliation of Beginning and Ending Aggregate Carrying Amount of Asset Retirement Obligation Current and Noncurrent) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Asset Retirement Obligation [Abstract]
Balance at end of year	$ 875,728		$ 880,003		$ 751,583
Current portion of liability at end of year	(34,202)	[1]	(27,515)	[1]
Noncurrent portion of liability at end of year	$ 841,526		$ 852,488

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