Stock incentive plans - Plans (Details) - shares |
Jan. 01, 2018 |
Sep. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|---|
| 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 | |||
| Stock incentive plans | |||
| Number of options outstanding | 405,000 | 1,283,000 | |
| Stock options | 2011 Plan | |||
| Stock incentive plans | |||
| Number of options outstanding | 302,000 | ||
| RSUs | 2011 Plan | |||
| Stock incentive plans | |||
| RSUs outstanding | 3,265,000 |