v3.26.1
Property, plant and equipment - Detail net of accumulated depreciation and impairment (Details) - USD ($)
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year $ 487,196,000  
Property, plant and equipment at end of the year 486,678,000 $ 487,196,000
Land and Buildings    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 58,562,000  
Property, plant and equipment at end of the year 60,271,000 58,562,000
Plant and Machinery    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 276,356,000  
Property, plant and equipment at end of the year 262,658,000 276,356,000
Other Fixtures, Tools and Furniture    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 8,556,000  
Property, plant and equipment at end of the year 9,110,000 8,556,000
Property, Plant and Equipment in the Course of Construction    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 43,962,000  
Property, plant and equipment at end of the year 47,627,000 43,962,000
Mineral Reserves    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 66,663,000  
Property, plant and equipment at end of the year 63,126,000 66,663,000
Other Items of Property, Plant and Equipment    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 1,030,000  
Property, plant and equipment at end of the year 4,910,000 1,030,000
Other Items of Leased Plant and machinery    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 18,539,000  
Property, plant and equipment at end of the year 19,401,000 18,539,000
Other Items of Leased Land and Buildings    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 13,527,000  
Property, plant and equipment at end of the year 19,575,000 13,527,000
Gross carrying amount    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 1,703,354,000 1,699,092,000
Additions 83,415,000 102,471,000
Disposals and other (58,569,000) (34,109,000)
Transfers from/(to) other accounts (642,000)  
Exchange differences 132,632,000 (64,100,000)
Property, plant and equipment at end of the year 1,860,190,000 1,703,354,000
Gross carrying amount | Land and Buildings    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 226,048,000 181,037,000
Additions 38,000 65,000
Disposals and other (2,116,000) (97,000)
Transfers from/(to) other accounts 2,032,000 51,924,000
Exchange differences 22,841,000 (6,881,000)
Property, plant and equipment at end of the year 248,843,000 226,048,000
Gross carrying amount | Plant and Machinery    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 1,214,411,000 1,197,462,000
Additions 545,000 3,415,000
Disposals and other (47,295,000) (28,173,000)
Transfers from/(to) other accounts 75,586,000 87,623,000
Exchange differences 93,792,000 (45,916,000)
Property, plant and equipment at end of the year 1,337,039,000 1,214,411,000
Gross carrying amount | Other Fixtures, Tools and Furniture    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 17,477,000 7,205,000
Additions 521,000 5,693,000
Disposals and other (775,000) (993,000)
Transfers from/(to) other accounts 289,000 6,369,000
Exchange differences 2,177,000 (797,000)
Property, plant and equipment at end of the year 19,689,000 17,477,000
Gross carrying amount | Property, Plant and Equipment in the Course of Construction    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 66,032,000 145,206,000
Additions 66,987,000 76,097,000
Disposals and other (57,000)  
Transfers from/(to) other accounts (78,529,000) (148,021,000)
Exchange differences 5,333,000 (7,250,000)
Property, plant and equipment at end of the year 59,766,000 66,032,000
Gross carrying amount | Mineral Reserves    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 69,714,000 67,091,000
Transfers from/(to) other accounts (3,377,000) 2,700,000
Exchange differences 365,000 (77,000)
Property, plant and equipment at end of the year 66,702,000 69,714,000
Gross carrying amount | Other Items of Property, Plant and Equipment    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 29,712,000 33,706,000
Additions 516,000 150,000
Disposals and other (37,000)  
Transfers from/(to) other accounts 3,357,000 (3,813,000)
Exchange differences 1,247,000 (331,000)
Property, plant and equipment at end of the year 34,795,000 29,712,000
Gross carrying amount | Other Items of Leased Plant and machinery    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 51,524,000 41,314,000
Additions 7,635,000 13,201,000
Disposals and other (4,727,000) (4,579,000)
Transfers from/(to) other accounts   3,218,000
Exchange differences 4,065,000 (1,630,000)
Property, plant and equipment at end of the year 58,497,000 51,524,000
Gross carrying amount | Other Items of Leased Land and Buildings    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year 28,436,000 26,071,000
Additions 7,173,000 3,850,000
Disposals and other (3,562,000) (267,000)
Exchange differences 2,812,000 (1,218,000)
Property, plant and equipment at end of the year 34,859,000 28,436,000
Accumulated depreciation    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (1,000,207,000) (997,127,000)
Disposals and other 43,522,000 30,959,000
Transfers from/(to) other accounts 80,000  
Exchange differences (88,082,000) 40,950,000
Depreciation and amortization for the period (83,035,000) (74,989,000)
Property, plant and equipment at end of the year (1,127,722,000) (1,000,207,000)
Accumulated depreciation | Land and Buildings    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (133,167,000) (119,009,000)
Disposals and other 2,116,000 101,000
Transfers from/(to) other accounts 64,000 (15,742,000)
Exchange differences (11,768,000) 4,486,000
Depreciation and amortization for the period (2,934,000) (3,003,000)
Property, plant and equipment at end of the year (145,689,000) (133,167,000)
Accumulated depreciation | Plant and Machinery    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (801,564,000) (821,272,000)
Disposals and other 33,455,000 25,847,000
Transfers from/(to) other accounts 195,000 20,285,000
Exchange differences (70,610,000) 33,987,000
Depreciation and amortization for the period (68,832,000) (60,411,000)
Property, plant and equipment at end of the year (907,356,000) (801,564,000)
Accumulated depreciation | Other Fixtures, Tools and Furniture    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (5,993,000) (1,149,000)
Disposals and other 255,000 165,000
Transfers from/(to) other accounts (68,000) (4,981,000)
Exchange differences (724,000) 361,000
Depreciation and amortization for the period (273,000) (389,000)
Property, plant and equipment at end of the year (6,803,000) (5,993,000)
Accumulated depreciation | Mineral Reserves    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (3,051,000) (2,840,000)
Depreciation and amortization for the period (525,000) (211,000)
Property, plant and equipment at end of the year (3,576,000) (3,051,000)
Accumulated depreciation | Other Items of Property, Plant and Equipment    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (10,146,000) (10,317,000)
Disposals and other 37,000  
Exchange differences (1,068,000) 353,000
Depreciation and amortization for the period (166,000) (182,000)
Property, plant and equipment at end of the year (11,343,000) (10,146,000)
Accumulated depreciation | Other Items of Leased Plant and machinery    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (32,204,000) (30,244,000)
Disposals and other 4,097,000 4,579,000
Transfers from/(to) other accounts (111,000) 438,000
Exchange differences (2,608,000) 1,234,000
Depreciation and amortization for the period (7,672,000) (8,211,000)
Property, plant and equipment at end of the year (38,498,000) (32,204,000)
Accumulated depreciation | Other Items of Leased Land and Buildings    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (14,082,000) (12,296,000)
Disposals and other 3,562,000 267,000
Exchange differences (1,304,000) 529,000
Depreciation and amortization for the period (2,633,000) (2,582,000)
Property, plant and equipment at end of the year (14,457,000) (14,082,000)
Impairment    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (215,951,000) (200,568,000)
Disposals and other 15,092,000 1,342,000
Exchange differences (17,029,000) 8,215,000
Impairment losses for the period (27,902,000) (24,940,000)
Property, plant and equipment at end of the year (245,790,000) (215,951,000)
Impairment | Land and Buildings    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (34,319,000) (22,680,000)
Transfers from/(to) other accounts   (11,166,000)
Exchange differences (2,104,000) 415,000
Impairment losses for the period (6,460,000) (888,000)
Property, plant and equipment at end of the year (42,883,000) (34,319,000)
Impairment | Plant and Machinery    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (136,491,000) (77,617,000)
Disposals and other 14,078,000 1,342,000
Transfers from/(to) other accounts (19,011,000) (45,529,000)
Exchange differences (12,054,000) 3,418,000
Impairment losses for the period (13,547,000) (18,105,000)
Property, plant and equipment at end of the year (167,025,000) (136,491,000)
Impairment | Other Fixtures, Tools and Furniture    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (2,928,000) (2,752,000)
Disposals and other 384,000  
Transfers from/(to) other accounts   877,000
Exchange differences (402,000) 299,000
Impairment losses for the period (830,000) (1,352,000)
Property, plant and equipment at end of the year (3,776,000) (2,928,000)
Impairment | Property, Plant and Equipment in the Course of Construction    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (22,070,000) (78,150,000)
Transfers from/(to) other accounts 19,011,000 55,817,000
Exchange differences (2,400,000) 4,047,000
Impairment losses for the period (6,680,000) (3,784,000)
Property, plant and equipment at end of the year (12,139,000) (22,070,000)
Impairment | Other Items of Property, Plant and Equipment    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (18,536,000) (18,542,000)
Exchange differences (6,000) 6,000
Property, plant and equipment at end of the year (18,542,000) (18,536,000)
Impairment | Other Items of Leased Plant and machinery    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (781,000)  
Disposals and other 630,000  
Exchange differences (63,000) 30,000
Impairment losses for the period (385,000) (811,000)
Property, plant and equipment at end of the year (599,000) (781,000)
Impairment | Other Items of Leased Land and Buildings    
Reconciliation of changes in property, plant and equipment [abstract]    
Property, plant and equipment at beginning of the year (827,000) (827,000)
Property, plant and equipment at end of the year $ (827,000) $ (827,000)