| Revenue recognition - Future Estimated Deferred License Revenue (Details) - Deferred license revenue $ in Thousands | Dec. 31, 2019  USD ($) | 
|---|---|
| 2020 | $ 205 | 
| 2021 | 205 | 
| 2022 | 181 | 
| 2023 | 276 | 
| 2024 | 116 | 
| Thereafter | 385 | 
| Total future estimated deferred license revenue | $ 1,368 | 
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- Definition Revenue Remaining Performance Obligation Next Twelve Months Amount. No definition available. 
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- Definition Amount of license fees to be received in after next fifth twelve months following latest statement of financial position date. No definition available. 
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- Definition Amount of license fees to be received in next fourth twelve months following latest statement of financial position date. No definition available. 
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- Definition Amount of license fees to be received in next third twelve months following latest statement of financial position date. No definition available. 
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- Definition Amount of license fees to be received in next second twelve months following latest statement of financial position date. No definition available. 
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- Definition Amount of license fees to be received in next twelve months following latest statement of financial position date. No definition available. 
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- 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 
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- Details 
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