| Revenue from contracts with customers (Details 3) - License [Member] $ in Thousands | Dec. 31, 2018  USD ($) | 
|---|---|
| 2019 | $ 171 | 
| 2020 | 154 | 
| 2021 | 154 | 
| 2022 | 154 | 
| 2023 | 154 | 
| Thereafter | 392 | 
| Total future estimated deferred license revenue | $ 1,179 | 
| X | ||||||||||
| 
- Definition Amount of license fees to be received in remainder of fiscal year. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount of license fees to be received in after next fifth twelve months following latest statement of financial position date. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount of license fees to be received in next fourth twelve months following latest statement of financial position date. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount of license fees to be received in next third twelve months following latest statement of financial position date. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount of license fees to be received in next second twelve months following latest statement of financial position date. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount of license fees to be received in next twelve months following latest statement of financial position date. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount of transaction price allocated to performance obligation that has not been recognized as revenue. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
 | 
| X | ||||||||||
| 
- Details 
 |