Segment Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) item	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Segment Information
Operating revenues	$ 99,207	$ 100,905	$ 96,187	$ 97,114	$ 99,631	$ 97,252	$ 96,784	$ 97,072	$ 393,413	$ 390,739	$ 391,150
Depreciation and amortization									87,879	78,014	77,301
Operating income (loss)	3,888	$ 4,195	$ 5,260	$ 5,919	7,821	$ 6,620	$ 7,892	$ 8,138	19,262	30,471	41,771
Capital expenditures									98,442	103,706	93,041
Assets	799,695				796,724				$ 799,695	796,724	771,724
Number of reportable segments | item									2
Telecommunications
Segment Information
Operating revenues									$ 383,767	381,013	389,168
Depreciation and amortization									85,643	76,325	76,935
Operating income (loss)									20,161	30,683	41,907
Capital expenditures									97,838	103,588	92,742
Assets	777,139				772,168				777,139	772,168	752,702
Data Center Colocation Services
Segment Information
Operating revenues									11,094	10,737	2,188
Depreciation and amortization									2,236	1,689	366
Operating income (loss)									(899)	(212)	(136)
Capital expenditures									604	118	299
Assets	22,556				24,556				22,556	24,556	19,022
Parent Company
Segment Information
Assets	$ 307,699				$ 304,534				307,699	304,534
Intersegment Elimination
Segment Information
Operating revenues									$ (1,448)	$ (1,011)	$ (206)