Reporting Segments (Assets by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 512,962	$ 528,423	$ 528,423
Capital expenditures	704	46,893
Production
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	54,799	58,623
Capital expenditures	3	441
Midstream
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	455,388	468,656
Capital expenditures	701	46,452
Corporate
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 2,775	$ 1,144