Consolidated Statements of Income - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
	Apr. 30, 2013	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenue		$ 76,963	$ 63,716	$ 52,886	$ 55,054	$ 55,365	$ 54,045	$ 54,881	$ 56,217	$ 248,619	$ 220,508	$ 211,661
Operating expense:
Network and facilities expense (excluding depreciation and amortization)		46,427	34,858	21,295	22,765	23,960	23,016	23,129	24,890	125,345	94,995	94,867
Operations		8,204	7,955	7,391	7,620	7,355	7,432	7,202	7,307	31,170	29,296	28,595
Sales and marketing		776	690	765	643	722	1,048	818	676	2,874	3,264	5,554
General and administrative		4,363	4,648	4,942	4,555	4,141	3,645	5,254	3,800	18,508	16,840	18,772
Depreciation and amortization		3,255	2,894	2,600	2,643	2,681	2,985	3,010	3,141	11,392	11,817	14,652
(Gain) loss on sale of property and equipment		10	(4)	(149)	33	(31)	2	(31)		(110)	(60)	192
Loss (gain) on sale of Americas data assets	$ (28,800)								1,081		1,081	(28,791)
Total operating expense		63,035	51,041	36,844	38,259	38,828	38,128	39,382	40,895	189,179	157,233	133,841
Income from operations		13,928	12,675	16,042	16,795	16,537	15,917	15,499	15,322	59,440	63,275	77,820
Other (income) expense:
Interest expense (income)		(7)	9	11	16	14	18	17	2	29	51	(6)
Other (income) expense					(1,290)			(2)		(1,290)	(2)	4
Total other (income) expense		(7)	9	11	(1,274)	14	18	15	2	(1,261)	49	(2)
Income before provision for income taxes		13,935	12,666	16,031	18,069	16,523	15,899	15,484	15,320	60,701	63,226	77,822
Provision for income taxes		5,255	4,399	6,031	6,887	6,417	6,123	6,036	6,127	22,572	24,703	13,524
Income from continuing operations										38,129	38,523	64,298
Loss from discontinued operations, net of provision for income taxes												(3,808)
Loss on sale of discontinued operations, net of provision for income taxes	$ 4,800											(4,837)
Net income		$ 8,680	$ 8,267	$ 10,000	$ 11,182	$ 10,106	$ 9,776	$ 9,448	$ 9,193	$ 38,129	$ 38,523	$ 55,653
Earnings per share- continuing operations:
Basic										$ 1.13	$ 1.17	$ 1.99
Diluted										1.12	1.15	1.97
Loss per share- discontinued operations:
Basic												(0.27)
Diluted												(0.27)
Earnings per share- net income:
Basic		$ 0.26	$ 0.25	$ 0.30	$ 0.33	$ 0.30	$ 0.30	$ 0.29	$ 0.28	1.13	1.17	1.72
Diluted		$ 0.25	$ 0.24	$ 0.29	$ 0.33	$ 0.30	$ 0.29	$ 0.28	$ 0.28	$ 1.12	$ 1.15	$ 1.71
Weighted average number of shares outstanding:
Basic		33,843	33,620	33,568	33,496	33,316	33,115	32,832	32,273	33,633,000	32,887,000	32,306,000
Diluted		34,213	34,138	34,033	33,970	33,785	33,343	33,369	32,616	34,070,000	33,384,000	32,557,000