Income taxes - Valuation allowance for deferred tax assets (Details) - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
|
| Deferred Tax Assets, Valuation Allowance [Roll Forward] | ||
| Valuation allowance as of beginning of year | $ 221,629 | $ 161,890 |
| Increases recorded to income tax provision | 90,329 | 59,848 |
| (Decreases) increases recorded to equity | 77 | (109) |
| Valuation allowance as of end of year | $ 312,035 | $ 221,629 |