v3.8.0.1
Summary of significant accounting policies - Revenue recognition (Details)
12 Months Ended
Dec. 31, 2017
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