v3.26.1
Financial instruments and risk management - Classification (Details) - BRL (R$)
R$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Dec. 31, 2024
Level 1 | Lenzing Aktiengesellschaft (Indirect) | Foreign countries      
Disclosure of detailed information about financial instruments [line items]      
Non-current financial assets at fair value through other comprehensive income R$ 831,600 R$ 865,986  
Loans, financing and debentures      
Disclosure of detailed information about financial instruments [line items]      
Financial liabilities, at fair value 91,134,497 93,828,907  
Loans, financing and debentures | Bonds | Foreign countries | Fixed      
Disclosure of detailed information about financial instruments [line items]      
Financial liabilities, at fair value 39,077,766 42,223,976 R$ 36,655,663
Financial risks management      
Disclosure of detailed information about financial instruments [line items]      
Financial assets 41,801,679 43,060,725  
Financial liabilities 111,296,497 117,843,727  
Financial Liabilities, Net of Financial Assets 69,494,818 74,783,002  
Financial risks management | Financial liabilities at amortised cost, category [member]      
Disclosure of detailed information about financial instruments [line items]      
Financial liabilities 102,714,740 108,502,378  
Financial risks management | Financial liabilities at amortised cost, category [member] | Trade accounts payable      
Disclosure of detailed information about financial instruments [line items]      
Financial liabilities 4,981,256 5,141,386  
Financial risks management | Financial liabilities at amortised cost, category [member] | Loans, financing and debentures      
Disclosure of detailed information about financial instruments [line items]      
Financial liabilities 90,735,617 94,801,257  
Financial risks management | Financial liabilities at amortised cost, category [member] | Lease liabilities      
Disclosure of detailed information about financial instruments [line items]      
Financial liabilities 6,763,902 6,929,890  
Financial risks management | Financial liabilities at amortised cost, category [member] | Dividends payable      
Disclosure of detailed information about financial instruments [line items]      
Financial liabilities 12,855 1,393,121  
Financial risks management | Financial liabilities at amortised cost, category [member] | Other liabilities      
Disclosure of detailed information about financial instruments [line items]      
Financial liabilities 221,110 236,724  
Financial risks management | At fair value through profit or loss      
Disclosure of detailed information about financial instruments [line items]      
Financial liabilities 8,581,757 9,341,349  
Financial risks management | At fair value through profit or loss | Derivative financial instruments      
Disclosure of detailed information about financial instruments [line items]      
Financial liabilities 8,581,757 9,341,349  
Financial assets at amortised cost, category [member] | Financial risks management      
Disclosure of detailed information about financial instruments [line items]      
Financial assets 18,537,681 22,335,429  
Financial assets at amortised cost, category [member] | Cash and cash equivalents | Financial risks management      
Disclosure of detailed information about financial instruments [line items]      
Financial assets 12,176,019 15,179,753  
Financial assets at amortised cost, category [member] | Trade accounts receivable | Financial risks management      
Disclosure of detailed information about financial instruments [line items]      
Financial assets 5,766,623 6,560,607  
Financial assets at amortised cost, category [member] | Other assets | Financial risks management      
Disclosure of detailed information about financial instruments [line items]      
Financial assets 595,039 595,069  
At fair value through other comprehensive income | Other investments | Level 3 | At fair value      
Disclosure of detailed information about financial instruments [line items]      
Non-current financial assets at fair value through other comprehensive income 32,924 35,195  
At fair value through other comprehensive income | Financial risks management      
Disclosure of detailed information about financial instruments [line items]      
Financial assets 864,524 901,181  
At fair value through other comprehensive income | Investments (2) | Financial risks management      
Disclosure of detailed information about financial instruments [line items]      
Financial assets 864,524 901,181  
At fair value through profit or loss | Marketable securities | Level 1 | At fair value      
Disclosure of detailed information about financial instruments [line items]      
Financial assets 1,298,243 1,274,439  
At fair value through profit or loss | Marketable securities | Level 2 | At fair value      
Disclosure of detailed information about financial instruments [line items]      
Financial assets 9,205,472 8,978,015  
At fair value through profit or loss | Financial risks management      
Disclosure of detailed information about financial instruments [line items]      
Financial assets 22,399,474 19,824,115  
At fair value through profit or loss | Derivative financial instruments | Financial risks management      
Disclosure of detailed information about financial instruments [line items]      
Financial assets 11,895,759 9,571,661  
At fair value through profit or loss | Marketable securities | Financial risks management      
Disclosure of detailed information about financial instruments [line items]      
Financial assets R$ 10,503,715 R$ 10,252,454