Stock-based compensation - Additional Information (Details) - USD ($)
|
3 Months Ended |
12 Months Ended |
Mar. 31, 2019 |
Mar. 31, 2020 |
Dec. 31, 2018 |
Dec. 31, 2017 |
| Service-based Stock Options |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Unrecognized stock-based compensation cost |
|
$ 3,300,000
|
|
|
| Unrecognized stock-based compensation cost, expected weighted-average period of recognition |
|
2 years 2 months 1 day
|
|
|
| Maximum contractual life |
|
10 years
|
|
|
| Expected dividend yield |
0.00%
|
0.00%
|
0.00%
|
0.00%
|
| Performance-based and Market-based Stock Options |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Unrecognized stock-based compensation cost |
|
$ 0
|
|
|
| RSA |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Unvested shares outstanding (in shares) |
|
1,128,789
|
|
|
| RSAs and RSUs |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Unrecognized stock-based compensation cost, expected weighted-average period of recognition |
|
2 years 4 months 24 days
|
|
|
| Unvested shares outstanding (in shares) |
2,786,398
|
2,311,768
|
2,036,124
|
|
| Unrecognized stock-based compensation cost |
|
$ 25,000,000
|
|
|
| 2016 Plan |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Number of shares authorized (in shares) |
|
13,457,391
|
|
|
| Shares available for grant (in shares) |
|
7,643,774
|
|
|
| 2014 Plan |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Number of options and awards outstanding (in shares) |
|
1,471,032
|
|
|