Long-Term Liabilities (Other Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Long-Term Liabilities [Abstract]
Asset retirement obligations	$ 130,110	$ 139,821	$ 57,196
Long-term derivative liabilities	6,244	7,402
Other	444	469
Total Other Liabilities	$ 136,798	$ 147,692