| Contingencies and commitments - Universal Cells Research, Collaboration and License Agreement and Co-development and Co-commercialization agreement (Details) - Collaboration and license agreement - Universal Cells, Inc. - USD ($) | 1 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|
| Feb. 29, 2016 | Nov. 30, 2015 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2022 | |
| Contingencies and commitments | |||||
| Upfront license and start-up fees | $ 2,500,000 | ||||
| Milestone payments | $ 3,000,000 | $ 200,000 | $ 900,000 | ||
| First milestone payment | $ 500,000 | ||||
| Second milestone payment | 600,000 | ||||
| Third milestone payment | 400,000 | ||||
| Maximum | |||||
| Contingencies and commitments | |||||
| Milestone payment accrued but not yet paid | $ 1,800,000 | ||||
| X | ||||||||||
| 
- Definition The amount of milestone payment accrued but not yet paid. No definition available. 
 | 
| X | ||||||||||
| 
- Definition The amount of milestone payment. No definition available. 
 | 
| X | ||||||||||
| 
- Definition The amount of milestone payment three. No definition available. 
 | 
| X | ||||||||||
| 
- Definition The amount of milestone payment two. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Represents the amount of milestone payments made by the entity under the license agreement. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Represents the amount of upfront and start-up fees paid. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
 | 
| X | ||||||||||
| 
- Details 
 | 
| X | ||||||||||
| 
- Details 
 | 
| X | ||||||||||
| 
- Details 
 |