Summary of significant accounting policies - Revenue recognition - Terms of contracts (Details)	9 Months Ended
	Sep. 30, 2019 item
Minimum
Revenue recognition
Payment terms	30 days
Maximum
Revenue recognition
Payment terms	60 days
Military and retail
Revenue recognition
Cancellation period of renewal option prior to end of current contract period	5 days
Multifamily
Revenue recognition
Number of performance obligations	2
Multifamily | Minimum
Revenue recognition
Initial term of the arrangement	3 years
Multifamily | Maximum
Revenue recognition
Initial term of the arrangement	5 years
DAS license agreements | Minimum
Revenue recognition
Initial term of the arrangement	5 years
DAS license agreements | Maximum
Revenue recognition
Initial term of the arrangement	20 years
Wholesale-Wi-Fi | Minimum
Revenue recognition
Initial term of the arrangement	1 year
Wholesale-Wi-Fi | Maximum
Revenue recognition
Initial term of the arrangement	3 years