Segment Information - Revenue Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Information on revenue, net of intersegment eliminations, by product group
Revenue	$ 96,780	$ 97,848	$ 99,541	$ 98,794	$ 99,207	$ 100,905	$ 96,187	$ 97,114	$ 392,963	$ 393,413	$ 390,739
Local voice and other retail services
Information on revenue, net of intersegment eliminations, by product group
Revenue									326,864	325,889	322,231
Wholesale carrier data services
Information on revenue, net of intersegment eliminations, by product group
Revenue									53,664	56,430	57,771
Data center
Information on revenue, net of intersegment eliminations, by product group
Revenue									$ 12,435	$ 11,094	10,737
Proceeds from the sale of equipment											$ 400