Stock incentive plans - Compensation expense (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Recognized stock-based compensation expense | |||
| Total stock-based compensation expense | $ 12,805 | $ 9,398 | $ 7,164 |
| Stock-based compensation expense capitalized | 727 | 778 | |
| Network operations | |||
| Recognized stock-based compensation expense | |||
| Total stock-based compensation expense | 2,144 | 1,504 | 1,356 |
| Development and technology | |||
| Recognized stock-based compensation expense | |||
| Total stock-based compensation expense | 1,070 | 731 | 600 |
| Selling and marketing | |||
| Recognized stock-based compensation expense | |||
| Total stock-based compensation expense | 1,842 | 3,411 | 2,017 |
| General and administrative | |||
| Recognized stock-based compensation expense | |||
| Total stock-based compensation expense | $ 7,749 | $ 3,752 | $ 3,191 |