Segment reporting - Sales by product line (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Disclosure of products and services [abstract] | |||
| Sales | $ 1,335,121 | $ 1,643,939 | $ 1,650,034 |
| Silicon Metal Product Line | |||
| Disclosure of products and services [abstract] | |||
| Sales | 430,155 | 726,650 | 722,226 |
| Manganese Alloys Product Line | |||
| Disclosure of products and services [abstract] | |||
| Sales | 357,724 | 332,845 | 259,197 |
| Ferrosilicon Product Line | |||
| Disclosure of products and services [abstract] | |||
| Sales | 282,560 | 272,386 | 330,946 |
| Other Silicon Based Alloys Product Line | |||
| Disclosure of products and services [abstract] | |||
| Sales | 115,823 | 131,744 | 159,441 |
| Silica Fume Product Line | |||
| Disclosure of products and services [abstract] | |||
| Sales | 27,705 | 31,323 | 33,804 |
| Other Product Lines | |||
| Disclosure of products and services [abstract] | |||
| Sales | $ 121,154 | $ 148,991 | $ 144,420 |