Reporting Segments - Reconciliation of Segment Operating Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Reconciliation of segment operating income to net income (loss):
Segment operating income	$ 10,505	$ 9,588	$ 21,419	$ 9,961
General and administrative expense	(6,919)	(6,353)	(12,084)	(11,962)
Unit-based compensation expense	(1,347)	(780)	(2,785)	(1,320)
Interest expense, net	(2,780)	(1,896)	(5,379)	(3,779)
Other expense	(1,254)		(1,524)
Net income (loss)	(1,795)	559	(353)	(7,100)	$ (3,040)
Production
Reconciliation of segment operating income to net income (loss):
Segment operating income	1,367	3,743	2,406	4,808
Midstream
Reconciliation of segment operating income to net income (loss):
Segment operating income	$ 9,138	$ 5,845	$ 19,013	$ 5,153