Stock incentive plans - Activity related to stock options (Details) - Stock options - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands |
12 Months Ended |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
| Shares |
|
|
|
| Outstanding, at the beginning of the period |
1,498
|
276
|
|
| Granted |
2,515
|
1,226
|
|
| Exercised |
(40)
|
|
|
| Forfeited and canceled |
(14)
|
(4)
|
|
| Outstanding, at the end of the period |
3,959
|
1,498
|
276
|
| Vested and expected to vest |
3,959
|
|
|
| Exercisable |
881
|
|
|
| Weighted-average exercise price |
|
|
|
| Outstanding, at the beginning of the period |
$ 2.48
|
$ 1.38
|
|
| Granted |
10.40
|
2.48
|
|
| Exercised |
2.57
|
|
|
| Forfeited and canceled |
4.79
|
1.93
|
|
| Outstanding, at the end of the period |
7.46
|
$ 2.48
|
$ 1.38
|
| Vested and expected to vest |
7.46
|
|
|
| Exercisable at the end of the period |
$ 2.69
|
|
|
| Weighted-average remaining contractual term |
|
|
|
| Weighted-average remaining contractual term |
8 years 9 months 15 days
|
8 years 11 months 5 days
|
9 years 2 months 9 days
|
| Vested and expected to vest |
8 years 9 months 15 days
|
|
|
| Exercisable |
8 years 7 days
|
|
|
| Aggregate intrinsic value |
|
|
|
| Outstanding, at the beginning of the period |
$ 4,146
|
$ 89
|
|
| Outstanding, at the end of the period |
35,984
|
$ 4,146
|
$ 89
|
| Vested and expected to vest |
35,984
|
|
|
| Exercisable |
$ 12,205
|
|
|
| Term of award |
10 years
|
|
|
| Vesting period |
4 years
|
|
|
| Weighted-average grant date fair value per share |
$ 7.03
|
$ 1.66
|
|
| Unrecognized stock-based compensation related to non-vested stock options |
$ 16,400
|
|
|
| Term in which unrecognized compensation expenses will be recognized |
|
2 years 11 months 16 days
|
|