Summary of Significant Accounting Policies (Accrued Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accrued interest	$ 16,996	$ 9,205
Accrued payroll	12,700	9,953
Asset Retirement Obligation, Current	4,430	4,763
Other accrued liabilities	3,529	5,478
Accrued liabilities	51,151	39,829
Property Tax
Taxes Payable, Current	$ 13,496	$ 10,430