Accrued Liabilities (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accrued Liabilities, Current [Abstract]
Lease operating expenses	$ 20,257	$ 20,709
Employee costs	10,854	31,451
Taxes	9,134	3,284
Interest	6,560	6,654
Third-party credits	4,040	2,825
Other	4,855	5,248
Total accrued liabilities	$ 55,700	$ 70,171