v3.8.0.1
Stock incentive plans - Compensation expense (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Recognized stock-based compensation expense      
Total stock-based compensation $ 14,215 $ 12,805 $ 9,398
Stock-based compensation expense capitalized 696 727 778
Network operations      
Recognized stock-based compensation expense      
Total stock-based compensation 2,174 2,144 1,504
Development and technology      
Recognized stock-based compensation expense      
Total stock-based compensation 1,068 1,070 731
Selling and marketing      
Recognized stock-based compensation expense      
Total stock-based compensation 2,060 1,842 3,411
General and administrative      
Recognized stock-based compensation expense      
Total stock-based compensation $ 8,913 $ 7,749 $ 3,752