Segment and Related Information - Schedule of revenue by geographic area (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
Revenue, net	$ 232,605	$ 229,653
United States \| Reportable Geographical Components
Segment Reporting, Asset Reconciling Item [Line Items]
Revenue, net	213,693	210,821
Other Countries \| Reportable Geographical Components
Segment Reporting, Asset Reconciling Item [Line Items]
Revenue, net	$ 18,912	$ 18,832

Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Name:	us-gaap_SalesRevenueNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration