| Line Item | Jun 30, 2026 | Mar 31, 2026 | Dec 31, 2025 | Sep 30, 2025 | Jun 30, 2025 | Mar 31, 2025 | Dec 31, 2024 | Sep 30, 2024 | Jun 30, 2024 | Mar 31, 2024 | Dec 31, 2023 | Sep 30, 2023 | Jun 30, 2023 | Mar 31, 2023 | Dec 31, 2022 | Sep 30, 2022 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Net sales | ||||||||||||||||
| YoY growth | +11.8% | +2.8% | -2.4% | -0.3% | ||||||||||||
| Cost of goods sold | ||||||||||||||||
| Gross profit | ||||||||||||||||
| % of revenue | 28.1% | 27.3% | 28.0% | 26.4% | ||||||||||||
| Operating expenses: | ||||||||||||||||
| Selling, general and administrative | ||||||||||||||||
| Research and development | ||||||||||||||||
| Adjustment to fair value of contingent consideration | ||||||||||||||||
| Profit on disposal of property, plant and equipment | ||||||||||||||||
| Total operating expenses | ||||||||||||||||
| % of revenue | -20.1% | -19.2% | -17.7% | -25.1% | ||||||||||||
| Operating income | ||||||||||||||||
| % of revenue | 8.1% | 8.1% | 10.3% | 1.3% | ||||||||||||
| Other income/(expense), net | ||||||||||||||||
| Interest income, net | ||||||||||||||||
| Income before income tax expense | ||||||||||||||||
| Income tax expense | ||||||||||||||||
| Net income | ||||||||||||||||
| % of revenue | 6.3% | 6.8% | 10.4% | 2.9% | ||||||||||||
| Net income attributable to non-controlling interests | — | — | ||||||||||||||
| Net income attributable to Innospec | — | — | ||||||||||||||
| % of revenue | 6.3% | 6.7% | — | — | ||||||||||||
| Basic | ||||||||||||||||
| Diluted |