Summary of significant accounting policies - Segment and geographic information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Primary revenue source
Number of reportable segment | segment									1
Revenue	$ 67,808	$ 65,253	$ 59,601	$ 58,159	$ 57,348	$ 53,655	$ 49,033	$ 44,333	$ 250,821	$ 204,369	$ 159,344
DAS
Primary revenue source
Revenue									95,216	80,552	58,182
Military/multifamily
Primary revenue source
Revenue									77,721	55,129	39,975
Wholesale-Wi-Fi
Primary revenue source
Revenue									47,481	31,529	22,221
Retail
Primary revenue source
Revenue									17,630	24,926	26,636
Advertising and other
Primary revenue source
Revenue									$ 12,773	$ 12,233	$ 12,330