Summary of significant accounting policies (Details 6) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 item	Dec. 31, 2013	Dec. 31, 2012
Primary revenue source
Number of reportable segments									1
Revenue	$ 33,627	$ 30,822	$ 28,396	$ 26,452	$ 28,766	$ 28,607	$ 26,239	$ 23,134	$ 119,297	$ 106,746	$ 102,506
Retail
Primary revenue source
Revenue									40,336	43,194	46,145
DAS
Primary revenue source
Revenue									38,259	32,681	30,751
Wholesale Wi-Fi
Primary revenue source
Revenue									15,209	17,261	18,744
Military
Primary revenue source
Revenue									4,486	1,260
Advertising and other
Primary revenue source
Revenue									$ 21,007	$ 12,350	$ 6,866