Stock incentive plans (Details) - shares |
Dec. 31, 2018 |
Sep. 30, 2018 |
|---|---|---|
| 2018 Plan | ||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Awards available for future grant | 3,816,895 | |
| 2015 Plan | ||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Awards available for future grant | 505,046 |