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Share-based compensation (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Jan. 31, 2023 | Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023 | Jun. 11, 2020 | Jun. 07, 2018 | Sep. 17, 2014
Share-based compensation |  |  |  |  |  |  |
Common stock reserved for issuance |  | 4,315,653 |  |  |  |  |
Stock option vesting period |  |  |  | 1 year |  |  |
Share-based compensation arrangement by share based payment award percentage of fair market person holding more then 10% voting stock |  | 110.00% |  |  |  |  |
Intrinsic value of options outstanding |  | $ 20.1 |  | $ 26.9 |  |  |
Intrinsic value of options unvested |  | 0.0 |  | $ 0.8 |  |  |
Intrinsic value of options exercised |  | $ 0.1 | $ 0.1 |  |  |  |
Stock Option Plan |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Stock option vesting period |  | 2 years |  |  |  |  |
Stock option vesting, percentage |  |  |  | 50.00% |  |  |
Option to purchase granted |  | 42,791 |  | 584,826 |  |  |
Options vested |  |  |  | 337,727 |  |  |
Minimum | Stock Option Plan |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Contractual term |  | 3 years |  |  |  |  |
Maximum | Stock Option Plan |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Contractual term |  | 10 years |  |  |  |  |
Tranche one |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Stock option vesting, percentage |  | 50.00% |  |  |  |  |
Tranche two |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Stock option vesting period |  | 1 year |  |  |  |  |
Stock option vesting, percentage |  | 50.00% |  |  |  |  |
2014 Stock Incentive Plan |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Common stock reserved for issuance |  |  |  |  |  |  | 3,000,000
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 |  |
Stock Option Plan |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Options granted |  | 42,791 |  | 602,526 |  |  |
Share-based awards at the granted |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Options granted |  | 42,791 | 484,701 |  |  |  |
Stock Appreciation Rights (SARs) |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Stock option vesting period | 6 months |  |  |  |  |  |
Option to purchase granted | 17,700 |  |  |  |  |  |
Selling, general and administrative expenses |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Share based compensation expense |  | $ 0.3 | $ 1.0 |  |  |  |

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