Fair value measurement (Details) - Recurring basis - USD ($) $ in Thousands |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Assets: | ||
| Money market accounts | $ 137,723 | $ 2,255 |
| Total assets | 137,723 | 2,255 |
| Liabilities: | ||
| Contingent consideration | 961 | |
| Total liabilities | 961 | |
| Level 1 | ||
| Assets: | ||
| Money market accounts | 137,723 | 2,255 |
| Total assets | 137,723 | 2,255 |
| Liabilities: | ||
| Contingent consideration | 0 | |
| Total liabilities | 0 | |
| Level 2 | ||
| Assets: | ||
| Money market accounts | 0 | 0 |
| Total assets | 0 | 0 |
| Liabilities: | ||
| Contingent consideration | 0 | |
| Total liabilities | 0 | |
| Level 3 | ||
| Assets: | ||
| Money market accounts | 0 | 0 |
| Total assets | 0 | $ 0 |
| Liabilities: | ||
| Contingent consideration | 961 | |
| Total liabilities | $ 961 |