Stockholders' equity - Stock-based compensation expenses (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
|
| Number of Options | ||||
| Stock-based compensation | $ 130 | $ 111 | $ 230 | $ 243 |
| Stock-based award plans | ||||
| Number of Options | ||||
| Unrecognized share-based compensation cost | 600 | $ 600 | ||
| Unrecognized share-based compensation - Weighted average period | 1 year 2 months 12 days | |||
| Location, Statement of Income, Balance [Axis]: us-gaap:GeneralAndAdministrativeExpense | ||||
| Number of Options | ||||
| Stock-based compensation | 92 | 83 | $ 161 | 175 |
| Location, Statement of Income, Balance [Axis]: us-gaap:ResearchAndDevelopmentExpense | ||||
| Number of Options | ||||
| Stock-based compensation | $ 38 | $ 28 | $ 69 | $ 68 |