Stock incentive plans - General (Details) - shares |
6 Months Ended | |
|---|---|---|
Jun. 30, 2017 |
Dec. 31, 2016 |
|
| Stock incentive plans | ||
| Number of options outstanding | 2,246,000 | 3,084,000 |
| 2011 Plan | ||
| Stock incentive plans | ||
| Annual percentage increase alternative, increase in common stock reserved for issuance as a percentage of common stock outstanding | 4.50% | |
| Annual fixed increase alternative, increase in shares of common stock reserved for issuance (in shares) | 3,000,000 | |
| Stock options | 2011 Plan | ||
| Stock incentive plans | ||
| Number of options outstanding | 1,605,731 | |
| RSUs | 2011 Plan | ||
| Stock incentive plans | ||
| RSUs outstanding | 3,677,294 |