Reporting Segments (Assets by Segment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 528,423	$ 539,705
Capital expenditures	46,893	19,534
Production
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	58,623	96,262
Capital expenditures	441	939
Midstream
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	468,656	440,675
Capital expenditures	46,452	18,595
Corporate
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 1,144	$ 2,768