Accrued Liabilities (Accrued Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts Payable and Accrued Liabilities, Current [Abstract]
Employee costs	$ 23,944	$ 24,632
Interest payable	17,747	6,568
Lease operating expenses	14,738	10,903
Taxes	11,563	7,308
Other	10,565	4,687
Total accrued liabilities	$ 78,557	$ 54,098