Financial commitments and contingent liabilities - Undrawn Commitments (Details) - USD ($) $ in Thousands |
Sep. 30, 2026 |
Dec. 31, 2025 |
|---|---|---|
| Commitments and Contingencies Disclosure [Abstract] | ||
| Definitive | $ 1,264,360 | $ 1,269,708 |
| Discretionary | 627,407 | 793,533 |
| Legal risk (definitive) | 47,032 | 47,235 |
| Total capital provision undrawn commitments | $ 1,938,799 | $ 2,110,476 |