Accrued Liabilities (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accrued Liabilities, Current [Abstract]
Lease operating expenses	$ 19,157	$ 17,220
Taxes	8,722	3,767
Employee costs	7,007	12,641
Interest payable	6,213	6,321
Third-party credits	2,954	3,326
Derivative settlements	278	0
Other	2,037	3,643
Total accrued liabilities	$ 46,368	$ 46,918