Accrued Liabilities (Accrued Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Accounts Payable and Accrued Liabilities, Current [Abstract]
Interest payable	$ 17,338	$ 6,568
Employee costs	14,599	24,632
Lease operating expenses	10,316	10,903
Taxes	5,433	7,308
Hedge settlements	0	160
Other	5,638	4,527
Total accrued liabilities	$ 53,324	$ 54,098