| Geographic information - Major Customers (Details) - customer | 12 Months Ended | ||
|---|---|---|---|
| Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | |
| Major Customers | |||
| Number of customers | 1 | 1 | 1 | 
| Revenues | Customer Concentration Risk | GlaxoSmithKline Intellectual Property Development Ltd | |||
| Major Customers | |||
| Concentration risk (as a percentage) | 100.00% | 100.00% | 100.00% | 
| X | ||||||||||
| 
- Definition Number of customers. No definition available. 
 | 
| X | ||||||||||
| 
- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- References No definition available. 
 | 
| X | ||||||||||
| 
- Details 
 | 
| X | ||||||||||
| 
- Details 
 | 
| X | ||||||||||
| 
- Details 
 |