Segment Information and Revenue by Channel (Revenue by Channel) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Information on revenue, net of intersegment eliminations, by product group
Revenue	$ 91,298	$ 99,541	$ 185,808	$ 198,335
Business services
Information on revenue, net of intersegment eliminations, by product group
Revenue	41,651	46,672	85,501	91,515
Consumer services
Information on revenue, net of intersegment eliminations, by product group
Revenue	33,831	35,952	68,093	72,159
Wholesale carrier data
Information on revenue, net of intersegment eliminations, by product group
Revenue	12,601	13,172	25,430	26,934
Other services
Information on revenue, net of intersegment eliminations, by product group
Revenue	$ 3,215	$ 3,745	$ 6,784	$ 7,727