Fair value measurements - Measurement of Fair Value of Major Asset and Liability classed (Details) - USD ($) $ in Thousands |
Jun. 30, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Assets: | ||
| Investments in equity | $ 67,743 | $ 57,948 |
| Investments in equity securities recorded at cost | 3,500 | 3,500 |
| Fair value, recurring | ||
| Assets: | ||
| Investments in equity | 64,243 | 54,448 |
| Total assets | 64,243 | 54,448 |
| Level 1 | Fair value, recurring | ||
| Assets: | ||
| Investments in equity | 0 | 0 |
| Total assets | 0 | 0 |
| Level 2 | Fair value, recurring | ||
| Assets: | ||
| Investments in equity | 0 | 0 |
| Total assets | 0 | 0 |
| Level 3 | Fair value, recurring | ||
| Assets: | ||
| Investments in equity | 0 | 0 |
| Total assets | 0 | 0 |
| Investments Measured at Net Asset Value | Fair value, recurring | ||
| Assets: | ||
| Investments in equity | 64,243 | 54,448 |
| Total assets | $ 64,243 | $ 54,448 |