Accrued Liabilities (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accrued Liabilities [Abstract]
Employee costs	$ 7,016	$ 17,832
Lease operating expenses	6,651	9,200
Taxes	6,343	3,450
Third-party credits	2,167	3,691
Derivative settlements	1,323	0
Interest payable	760	6,562
Other	7,124	5,827
Total accrued liabilities	$ 31,384	$ 46,562