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Stock-based compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands | 1 Months Ended | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Feb. 28, 2025 | Feb. 29, 2024 | Jul. 31, 2021 | Mar. 31, 2025 | Mar. 31, 2024 | Dec. 31, 2024 | May 31, 2023
Share-based compensation |  |  |  |  |  |  |
Intrinsic value of stock options exercised |  |  |  | $ 330 | $ 100 | $ 135 |
Weighted average grant-date fair value of stock options granted (in dollars per share) |  |  |  | $ 1.79 | $ 0.50 |  |
Total fair value of shares vested |  |  |  |  | $ 300 |  |
Stock-based compensation expense |  |  |  | $ 1,042 | $ 1,085 |  |
Unrecognized compensation expense |  |  |  | $ 3,000 |  |  |
Restricted Stock Units (RSUs) |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Weighted average recognition period |  |  |  | 1 year 3 months 18 days |  |  |
Weighted average grant-date fair value per share of units granted (in dollars per share) |  |  |  | $ 3.50 | $ 0.95 |  |
Total fair value of shares vested |  |  |  | $ 900 |  |  |
Unrecognized compensation expense related to units |  |  |  | $ 4,500 |  |  |
Restricted Stock Units (RSUs) | Minimum |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Vesting period |  |  |  | 1 year |  |  |
Restricted Stock Units (RSUs) | Maximum |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Vesting period |  |  |  | 3 years |  |  |
Option |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Weighted average recognition period |  |  |  | 1 year 1 month 6 days |  |  |
Class A Common stock |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Shares available for future issuance (in shares) |  |  |  | 28,866,867 |  |  |
2010 Plan |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Shares authorized (in shares) |  |  |  | 0 |  |  |
2021 Plan |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Shares authorized (in shares) |  |  |  | 5,531,001 |  |  |
Plan term |  |  | 10 years |  |  |  |
2021 Plan | Class A Common stock |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Shares authorized (in shares) |  |  | 4,200,000 |  |  |  |
Percentage of aggregate number of shares outstanding |  |  | 5.00% |  |  |  |
Maximum number of shares issuable upon exercise of stock option (in shares) |  |  | 33,900,000 |  |  |  |
Inducement Plan | Class A Common stock |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Shares available for future issuance (in shares) |  |  |  | 217,013 |  | 217,013 | 330,000
Additional shares authorized (in shares) | 476,000 | 225,000 |  |  |  |  |
2021 ESPP |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Plan term |  |  | 10 years |  |  |  |
Stock-based compensation expense |  |  |  | $ 100 | $ 100 |  |
2021 ESPP | Employee Stock |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Maximum percentage of payroll deduction |  |  | 15.00% |  |  |  |
Offering period |  |  | 6 months |  |  |  |
Maximum shares available for purchase per employee (in shares) |  |  | 100,000 |  |  |  |
Maximum value of shares available for purchase per employee |  |  | $ 25 |  |  |  |
Discount percentage from market price |  |  | 85.00% |  |  |  |
2021 ESPP | Class A Common stock |  |  |  |  |  |  |
Share-based compensation |  |  |  |  |  |  |
Shares authorized (in shares) |  |  | 400,000 |  |  |  |
Percentage of aggregate number of shares outstanding |  |  | 1.00% |  |  |  |
Maximum number of shares issuable upon exercise of stock option (in shares) |  |  | 6,300,000 |  |  |  |
Shares available for future issuance (in shares) |  |  |  | 1,206,897 |  |  |
Shares purchased under plan (in shares) |  |  |  | 127,335 |  |  |

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