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Related party transactions (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Aug. 31, 2016	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Related party transactions
Note receivable from affiliate		$ 6,800		$ 6,800		$ 8,000
Interest income		662	$ 846	1,339	$ 1,719
Unsecured Revolving Demand Promissory \| Valhi Inc
Related party transactions
Maximum loan amount	$ 25,000
Interest rate on loans repayment	1.00%
Principal due on demand effective date	Dec. 31, 2027
Unsecured Revolving Demand Promissory \| Related Party \| Valhi Inc
Related party transactions
Note receivable from affiliate		$ 6,800		6,800
Interest income				$ 400	$ 400