Reportable Segments (Assets by Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 465,841	$ 471,300
Upstream
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	126,773	118,083
Midstream
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 339,068	$ 353,217