Accrued Liabilities (Accrued Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accrued Liabilities [Abstract]
Employee costs	$ 24,632	$ 22,518
Lease operating expenses	10,903	7,346
Taxes	7,308	13,480
Interest Payable, Current	6,568	2,647
Hedge settlements	160	1,844
Other	3,591	3,898
Total accrued liabilities	$ 53,162	$ 51,733