Segment Information and Revenue by Product Group (Revenue by Product Group) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Information on revenue, net of intersegment eliminations, by product group
Revenue	$ 94,510	$ 98,794
Local voice and other retail services
Information on revenue, net of intersegment eliminations, by product group
Revenue	81,682	85,032
Wholesale carrier data services
Information on revenue, net of intersegment eliminations, by product group
Revenue	$ 12,828	$ 13,762

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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