Reporting Segments (Assets by Segment) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 464,396	$ 486,685
Capital expenditures	782	4,867
Production
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	48,162	53,556
Capital expenditures	103	11
Midstream
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	414,129	429,523
Capital expenditures	679	4,856
Corporate
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 2,105	$ 3,606