Stock incentive plans - Compensation expense (Details) - USD ($) $ in Thousands |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Recognized stock-based compensation expense | ||
| Total stock-based compensation expense | $ 3,126 | $ 3,044 |
| Stock-based compensation expense capitalized | 186 | 194 |
| Network operations | ||
| Recognized stock-based compensation expense | ||
| Total stock-based compensation expense | 537 | 546 |
| Development and technology | ||
| Recognized stock-based compensation expense | ||
| Total stock-based compensation expense | 278 | 270 |
| Selling and marketing | ||
| Recognized stock-based compensation expense | ||
| Total stock-based compensation expense | 473 | 426 |
| General and administrative | ||
| Recognized stock-based compensation expense | ||
| Total stock-based compensation expense | $ 1,838 | $ 1,802 |