Summary of significant accounting policies - Segment and geographic information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Primary revenue source
Number of reportable segment | segment			1
Revenue	$ 58,754	$ 64,707	$ 177,312	$ 199,734
Military/multifamily
Primary revenue source
Revenue	23,806	23,641	70,226	73,934
DAS
Primary revenue source
Revenue	21,877	23,714	66,287	75,431
Wholesale-Wi-Fi
Primary revenue source
Revenue	10,110	11,200	29,559	32,938
Retail
Primary revenue source
Revenue	2,060	3,646	7,387	11,419
Advertising and other
Primary revenue source
Revenue	$ 901	$ 2,506	$ 3,853	$ 6,012