Accrued Liabilities (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accrued Liabilities [Abstract]
Interest payable	$ 17,560	$ 6,745
Lease operating expenses	11,570	11,819
Employee costs	9,754	19,521
Taxes	4,139	3,404
Third-party credits	2,051	2,240
Derivative settlements	1,527	0
Other	6,363	4,794
Total accrued liabilities	$ 52,964	$ 48,523