Segment and Related Information - Schedule of identifiable assets by geographic area (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 114,624	$ 124,049
United States | Reportable Geographical Components
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	99,284	110,369
Other Countries | Reportable Geographical Components
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 15,340	$ 13,680