| Line Item | Jun 30, 2026 | Mar 31, 2026 | Jun 30, 2025 | Mar 31, 2025 |
|---|---|---|---|---|
| Revenue | ||||
| Total revenue | — | |||
| Operating expenses | ||||
| Total cost of sales | ||||
| Selling, general and administrative expenses | ||||
| Research and development expenses | ||||
| Restructuring and other expenses (income), net | ||||
| Total operating expenses | ||||
| % of revenue | 102.8% | — | ||
| Operating income (loss) | ||||
| % of revenue | -2.8% | — | ||
| Foreign currency gain (loss), net | ||||
| Other non-operating income (loss), net | ||||
| Interest income (expense), net | ||||
| Income (loss) before income taxes | ||||
| Income tax (expense) benefit | ||||
| Net income (loss) | ||||
| % of revenue | -2.9% | — | ||
| Less: Net income (loss) attributable to non-controlling interests | ||||
| Net income (loss) attributable to HMH Holding Inc. | ||||
| % of revenue | 2.9% | — | ||
| Net income (loss) per share of common stock (actual)—Basic (in dollars per share) | ||||
| Net income (loss) per share of Class A common stock (actual) — Diluted (in dollars per share) |