Accrued Liabilities (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued Liabilities [Abstract]
Employee costs	$ 17,832	$ 20,315
Lease operating expenses	9,200	12,756
Interest payable	6,562	6,635
Third-party credits	3,691	2,129
Taxes	3,450	1,378
Other	5,827	4,710
Total accrued liabilities	$ 46,562	$ 47,923