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Share-based compensation (Details) - USD ($) $ in Millions | 1 Months Ended | 9 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2025 | Sep. 30, 2025 | Sep. 30, 2024 | Dec. 31, 2024 | Jun. 12, 2024 | Jun. 11, 2020 | Jun. 07, 2018
Share-based compensation |  |  |  |  |  |  |
Aggregate common stock reserved for issuance | 6,704,335 | 6,704,335 |  |  |  |  |
Share-based compensation arrangement by share based payment award percentage of fair market Person holding more then 10% voting stock |  | 110.00% |  |  |  |  |
2018 Stock Incentive Plan |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Common stock reserved for issuance |  |  |  |  |  |  | 4,000,000
2020 Stock Incentive Plan |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Common stock reserved for issuance |  |  |  |  |  | 3,000,000 |
2024 Stock Incentive Plan |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Common stock reserved for issuance |  |  |  |  | 3,000,000 |  |
Stock Option Plan |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Stock option vesting period |  | 2 years |  |  |  |  |
Options granted under the Plans expire |  | 10 years |  |  |  |  |
Option to purchase granted |  | 459,630 |  | 135,603 |  |  |
Stock Option Plan | Tranche one |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Options vested |  | 68,490 |  | 111,975 |  |  |
Stock Option Plan | Tranche two |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Stock option vesting, percentage |  |  |  | 50.00% |  |  |
Stock Option Plan | Tranche three |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Stock option vesting period |  |  |  | 1 year |  |  |
Stock option vesting, percentage |  |  |  | 50.00% |  |  |
Stock Option Plan | Minimum |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Contractual term |  | 3 years |  |  |  |  |
Stock Option Plan | Maximum |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Contractual term |  | 10 years |  |  |  |  |
Incentive Stock Options |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Options granted under the Plans expire |  | 5 years |  |  |  |  |
Stock Appreciation Rights (SARs) |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Stock option vesting period | 2 years |  |  |  |  |  |
Option to purchase granted | 2,500 |  |  |  |  |  |
Selling, general and administrative expenses |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Share-based compensation expense |  | $ 0.6 | $ 0.8 |  |  |  |

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