Stock incentive plans - Compensation expense (Details) - USD ($) $ in Thousands |
3 Months Ended | |
|---|---|---|
Mar. 31, 2019 |
Mar. 31, 2018 |
|
| Recognized stock-based compensation expense | ||
| Total stock-based compensation expense | $ 2,344 | $ 3,126 |
| Stock-based compensation expense capitalized | 230 | 186 |
| Network operations | ||
| Recognized stock-based compensation expense | ||
| Total stock-based compensation expense | 506 | 537 |
| Development and technology | ||
| Recognized stock-based compensation expense | ||
| Total stock-based compensation expense | 303 | 278 |
| Selling and marketing | ||
| Recognized stock-based compensation expense | ||
| Total stock-based compensation expense | 529 | 473 |
| General and administrative | ||
| Recognized stock-based compensation expense | ||
| Total stock-based compensation expense | $ 1,006 | $ 1,838 |