Accrued Liabilities (Accrued Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Accrued Liabilities [Abstract]
Taxes	$ 12,899	$ 13,480
Employee costs	12,732	22,518
Lease operating expenses	8,861	7,346
Interest payable	6,981	2,647
Hedge settlements	1,649	1,844
Other	4,351	3,898
Total accrued liabilities	$ 47,473	$ 51,733