Accrued Liabilities (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Accrued Liabilities, Current [Abstract]
Employee costs	$ 10,526	$ 15,394
Lease operating expenses	10,047	10,075
Interest payable	6,684	6,524
Taxes	6,577	2,219
Third-party credits	2,149	2,998
Other	3,109	2,441
Total accrued liabilities	$ 39,092	$ 39,651