Segment Information and Revenue by Channel (Revenue by Channel) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Information on revenue, net of intersegment eliminations, by product group
Revenue	$ 91,013	$ 97,848	$ 276,821	$ 296,183
Business services
Information on revenue, net of intersegment eliminations, by product group
Revenue	41,860	44,797	127,363	136,312
Consumer services
Information on revenue, net of intersegment eliminations, by product group
Revenue	33,688	35,680	101,780	107,838
Wholesale carrier data
Information on revenue, net of intersegment eliminations, by product group
Revenue	12,567	13,440	37,997	40,373
Other services
Information on revenue, net of intersegment eliminations, by product group
Revenue	$ 2,898	$ 3,931	$ 9,681	$ 11,660